I am a firm believer in having a piano if you want to learn to play the piano (or have your child learn to play the piano)! You can't learn to ride a unicycle if all you have is a tricycle, but, yes, having a bicycle is a little help in learning the unicycle.
Reasons cited most as to why a real piano is not be feasible are space and money, with money's being the preponderant answer. Sometimes apartment dwellers or people whose work/school schedules require earphone use to avoid disturbing others is another valid reason.
If the choices are between learning to play on something other than a real piano and not learning to play at all, it's a no-brainer to use an electronic keyboard. Know, however, that you'll want a real piano very shortly into the learning process.
Keyboards in and of themselves aren't all bad! They have many "fun functions," such as weird sounds ("aliens"), sounds from other instruments, sounds for several pianos/organs/harpsichords, built-in rhythms/percussion, pre-loaded songs, and so on. They're fun to experiment with. And they're perfect to take to Grandma's.
Still and all, my advice is to go with a real piano and get an electronic just for fun.
If a real piano isn't feasible right now (cost, not enough floor space, need for headphones during practice), go with an electronic rather than put off lessons.
Here are my recommendations of features to seek, features that do no harm, features to avoid, and the brand I think you should give most serious consideration.
First, three caveats.
1. Read the spec list! Do not rely on the sales description!
It is likely, as you know, that things not included are not mentioned in the sales description (and certainly not in the spec list). Don't assume something that would seem to essential is included in the basic package.
For example, if the description lists "comes with earphones," one reasonably can expect there is a jack into which to plug the earphones. Butů.is there a way to hear the instrument's sound without earphones? That is, are there onboard speakers? If not, you'll need to hook up the keyboard to your own speakers or computer. (Is there a jack for this? Two or more? Are cables included?)
2. Do not rely on what a salesperson or a friend tells you!
3. Do not go by the photograph! It may "show available features," yet obscure this fact by revealing it in very, very small print and incomplete sentences at the end of a description. ("Stand optional," for example.)
Spec list, spec list!
1. Keyboard compass. The piano has 88 keys. High-end electronic keyboards have 88, also, but most keyboards that are bought for student or casual use have 61. Do not be fooled by a description of "full keyboard" or "complete keyboard."
Get at least 61 keys. This will take you through a great deal of literature. By the time you're playing Chopin and Beethoven, you'll have purchased (or rented) a real piano.
Fewer than 61 keys makes the electronic keyboard a toy and useless as an instrument for learning.
2. Key width. This should be the same as on a real piano. Some electronic keyboards have slim keys (especially small and/or cheap ones). Playing on one size at home and another size everywhere else will be a real detriment to learning. You must have keys that are the size of those on a real piano.
3. Touch-sensitive keys (also called "velocity"). These are a requirement. The harder you hit the key, the louder the sound, just as in a real piano. Do not scrimp here. Lack of touch-sensitive keys is the main reason people change from a keyboard to a real piano. Without being able to play some keys louder than other keys, it's impossible to play the melody louder than the accompaniment.
There is also something called "weighted keys." This is not the same as touch-sensitive keys. When keys are weighted, it feels more like playing real piano keys. (Real piano keys actually have disks of lead embedded.) If the instrument has weighted keys but not touch-sensitive keys, I suggest you pass this one by and keep looking.
4. Polyphony. This refers to how many notes can sound at once. The higher the number, the better. Low polyphony numbers mean that some notes in a chord "won't sound" because there "aren't enough circuits to give each note its own." For example, you could depress the keys for five Cs and hear only three of them. The other two notes would not sound, even though you are depressing the keys that should produce those notes.
5. Bench. Does one come with the keyboard? A piano bench is 19" high. If you don't have something 19" high, you need to get something that height (chair, stool, or even an end- or coffee table). A higher or lower seat will hinder learning, force (or allow) incorrect hand position, and cause tendonitis. Children, in particular, suffer if the seat is too low.
6. Stand. You must have a stand. You cannot put the instrument on a table or the arm of the sofa or in your lap.
Some keyboards include a stand. Very inexpensive keyboards usually do not.
Inexpensive stands are flimsy. For a child beginner, a flimsy stand may be perfectly adequate. I wouldn't recommend a flimsy stand for a teen or adult.
Many keyboards that come with stands come with flimsy stands. If the keyboard does not come with a stand, it is a good investment to choose a stand above the lowest price point (this shouldn't be more than $10-$15 more).
Inexpensive stands are usually X-shaped. Others are more like tables; these are more stable.
7. Music desk ("music stand"). Obviously, you need somewhere to put the music! Some cheap keyboards do not have a music desk! Specs, specs!
8. Power source. This is one of those things that one would expect as a matter of course but may not be included. Is there a way to plug the keyboard into the wall (through power source), or is it powered by batteries only? (How many batteries and what kind?) Both sources of power?
9. Speakers. You really need these to be in the unit to simulate where the sound comes from in a real piano, relative to where you're sitting when playing. Hooking the keyboard to speakers placed behind the player is confusing.
10. Reversion to default setting. This is not a good thing, but I mention it here because the reverse is the desirable feature.
Does turning off the unit cancel all customizations and revert to the default settings when turned on again, necessitate resetting everything when you turn on the instrument again? What must be reset? Turn volume up or down, select instrument sound, turn off percussion patterns and reverb, etc.?
Some keyboards have customized buttons that can be set. Others have a separate "piano" button that makes all changes needed for straight piano sound.
If you have to reset everything every time you fire up your electronic, this will eat into your joy of sitting down to play and sitting down when you have only a couple of minutes. Certainly, children will find making all these changes first a pain in the neck, and this will reduce their interest in playing and increase the hassle quotient.
Pedal. More than 98% of the time, the pedal will be only a sustain pedal ("damper pedal" on a real piano. This may be worth buying if you will be using the instrument for a long time. If the instrument does not come with a pedal, is there a port to add one later?
Auto off. Power saver.
Recorder. Some allow you to record something you play, for critical listening or for playing a duet with yourself! If you're composing and want to combine a violin solo with a piano accompaniment, record the violin part on the violin setting and play that back while you play the accompaniment on the piano setting.
MIDI capability. "Musical instrument digital interface" basically allows instruments (keyboards, guitars, flutes, violins, etc.) to work with a computer. If you want to set in notation the music you play on your keyboard, you will need MIDI capability (port, cables). You also will need notation software, such as Finale. Most students will not be interested in this feature.
If you want to download MIDI files from the Internet and play them through your keyboard's speakers (as opposed to your computer's or some other speakers; or an mp3 player), then MIDI capability will be required.
Auto-chords. This generally means playing one note and getting the entire chord instead.
Auto fill-in. This generally means generating an accompaniment by hitting only one key.
Both of these are fun for experimentation, and both usually come standard on any keyboard. Don't pay extra for these or choose a keyboard with these, at the expense of, say, high polyphony or touch-sensitive keys.
Split Key Mode. This means you can play one instrument sound on the upper end of the keyboard and another on the lower part. Usually the split point is Middle C. (Sometimes this is moveable, but often not.)
Dual Key Mode. This means you can combine two (sometimes three or more, but not usually) different sounds (example: xylophone + trumpet).
Powered by batteries only.
Lack of onboard speakers.
Lights that flash on/off on the keys themselves - unless the lights can be turned off. These are a distraction and not conducive to note-reading. (Yamaha EZ-200 has these. Ugh. The name's a dead give-away!)
Anything that "rolls up." Totally and utterly worthless. Not to mention totally and utterly frustrating. A scam.
Also, you won't need an "extended warranty." These are just an easy profit add-on for the seller. Anything electronic that is going to fail is going to fail very quickly, so an extension of the warranty period is useless.
When looking for an instrument, consider buying a used one. You'll get a lot more features for the same money as if you bought a new instrument. Check places like eBay and craigslist. Also your local want-ads and Pennysaver-type newspapers. Also keep an eye out for estate sales, though this is a long shot.
Many people start to learn the piano and discover it is not as easy as the late-night TV ads say it is! The result is that there are a lot of electronic keyboards floating around, not being used. Some people sell theirs.
And, of course, there are those who sell their keyboards because they've bought a real piano.
Some folks with an electronic do keep it as a second keyboard to take to Grandma's, to performances where a real piano is not available (band shell-in-the-park kinds of things), to fiddle around with all the sounds and rhythm features, etc.
Another place to look for a keyboard at a better price than straight retail is a place like Costco. Their selection will be very limited, however, and you probably will not find a keyboard with the features you want. But it's worth a look-see.
Several kinds of electronic keyboard-type instruments are often lumped together and called "keyboards," when, in fact, there are two distinct classes of electronic keyboards: synthesizers ("synths") and digital pianos.
Synthesizers create sound by manipulating electronic wave forms. Synthesizers are what you're buying when you get an "electronic keyboard." Examples: Yamaha and Casio.
Digital pianos' sounds are made by "sampling" the sounds of real piano. Digital pianos usually are purchased only by professionals because they are quite expensive, especially for a not-real piano. They are often used by stage bands because they're portable. They are also used by professional musicians for recording. Examples: Korg and Roland. While they hold their value, resale isn't going to be as lucrative as with a synth because most people won't even recognize the name, know it's a high-end instrument, know the sound is sampled not synthesized, and be willing to pay accordingly. Digital keyboards always have 88 touch-sensitive keys.
There is another Yamaha product of which you should be aware. It's called a Clavinova. While the piano sound tends to be better, it is still a synth. The top-of-the-line model is about $12,000 (in 2008). For that price you can get a lovely real piano! (Note: Sometimes these synths are "shaped like" a grand piano, curved side and all!)
Don't choose by low price. Be suspicious of a $20 keyboard. It's going to have a small compass, small-scale keys, and so on. Yamaha keyboards are consistently high in quality and practical features. They have high resale value. I recommend you look first at those. Casio also makes good keyboards, but you must read the spec list carefully.
I own a Yamaha PSR-300. I bought it for MIDI capability so I could "play music into" my computer and thus transform it to printed notation, using Finale software. Keys are not weighted but are touch sensitive and normal size. The compass is two octaves below Middle C to three octaves above it (61 notes). It has 32-voice polyphony. On-board speakers are mounted on either side of the keyboard. Music desk standard, but not stand (~$30). No metronome. Battery and plug-in power. MIDI ports. This has served me well. I have felt no need for a fancier model. I recommend this one. (Update, 2010: This model has been "renumbered" and is now YPT-300.)
A student of mine owns a Yamaha PSR-313 [YPT-313], in addition to a real piano, and is very pleased with it. This is the next level up from mine. He particularly likes the dedicated "gimme a piano" button and the various organ and harpsichord options. The keys are touch sensitive, 61-note compass, 32-note polyphony, on-board speakers. I also recommend this instrument. Yamaha considers it an "entry level" keyboard, but it will do everything a beginning student needs! This model sells for $150 on Yamaha's own website (in November, 2008), and you probably can get it for less elsewhere, especially if you buy used.
I think you will be quite happy with either of these.
If you have a regular electronic keyboard, there's a 99% probability that it will have at least one harpsichord setting, so you won't need to buy one of these.
Presently (2009), the cost of the Roland is about $5000.
My review of this instrument is in this file, at the bottom.