Other's I've seen but don't know where to find:
I can't tell you where to find the Mame64 project, because they were silly and embedded licensed roms. However, it works quite well for everything that isn't a vector-based game.
There's the horrendous datel GB emulator. It doesn't play GB sound, just this evil noise in place of it. It also doesn't allow custom chipsets.
There's a Sega game gear emulator, though it usually erroneously is called a master system emulator despite not doing that at all really. It only works on console.
There's a demo of a SNES emulator around, but it, quite terribly, plays only a very small number of games, most homebrews.
I there's an MSX emu as well. It was supposed to cap off at a certain memory mark, so you probably can't play metal gear 2. Still, awfully cool.
Other weird stuff are tracker and mp3 players. Again, you'll have to search around for them, but it can't be that hard.