Try out DrMD, its an AMAZING genesis/megadrive emulators (and remember to thank reesy!)
Also try:
Another world= It is an almost perfect (if not perfect) port of an amazing game.
Little John= A great NES emulator with a LOT of options
fGB32 f-day preview= A great gameboy/color emulator
fCOL32 f-day preview=A great colecovision emulator
MAME= Multi Arcade Machine Emulator, can emulate many (about 700) old arcade games, check the compatability list included with it for more details
Doom= A great port of doom (Supports doom I and II, but you need to get your own WAD files to play it)
Bolcataxian= An excellent homebrew verticle space shooter
Lacuna= Another excellent homebrew
Crazy Jack= Really fun homebrew game. This is permanently on my SMC.
Nazca Dream= A really excellent homebrew game with great graphics.
Fate= My VNS (VirtuaNovelSystem) game

It isn't close to finished yet and not many people have given me feedback on it, you can find it at
www.fategp.com. You will have to download VNS in order to play it.
All files mentioned should be available for download at
www.gp32x.de unless otherwise stated.