By electric pianos I mean Wurly, Tine, Rhodes, Reed, SA EP, FM EP, etc. How many are they? And how are they different? (Would be great if some song examples are provided.)
Electric pianos are (typically) vintage instruments that produce sound in a mechanical way, capturing the sound with an electro-magnetic transducer of some kind (much like the pickups of an electric guitar).
The first models of these type of instruments appeared in 40's and 50's and the technology become mainstream in the 60's and 70's with two most important "families" of electric pianos: the Fender Rhodes (struck tines) and the Wurlitzer, or "Wurli" (struck reeds). The Wikipedia Electric Pianos page explains this in more detail and points to the specific pages of these two instruments, where more details and audio examples can also be found.
At the end of the 70's Yamaha introduced a different type of instrument, an electric "grand piano" (thanks to @Brian THOMAS for calling attention to this prior omission and for the text of the following period). Yamaha CP70 was an example of a giggable grand piano (proper hammers and strings) but with pick-ups and no sound board. This actually sounded like a piano and was the only decent sounding choice until sampling pianos became widespread.
FM (Frequency Modulation) is a synthesis technique invented by Yamaha in the 80's and applied in the famous Yamaha DX7 synthesizer, used by so many bands of the 80's and a great part of the so called "80's sound". In particular an "FM piano" type of (synthesized) sound is quite characteristic.
SA (Structured Adaptative) is another synthesis technique, invented by Roland by the end of 80's, specifically to try to digitally recreate the sound of a(n acoustic) piano (unlike the technologies we've been talking about, that have their own characteristic sound and did not aimed to faithfully replicate the sound of an acoustic piano).
Both FM and SA are digital (purely electronic, not "electric") sound synthesis techniques (this excellent article tells the story and gives more details about these technologies).
That are and there were along time many different type of instruments that may fall in the category of electric/electronic pianos, but I think it's worth mentioning at least:
- the whole host of home and stage pianos based on sampling.
- the purely software based instruments with huge sampling libraries and a specific algorithms to try to emulate as faithfully as possible the dynamics of a real piano.