Genesis/Mega Drive - Picodrive
Sega CD/Sega Mega CD - Picodrive
Sega Master System - DrMDX (maybe AlexKidd2x, but I haven't tried it)
SNES - PocketSNES
MAME - MAME GP2X
TubroGrafx 16/PC Engine - GP2xengine
Capcom Play System 2 - CPS2emu
Neo Geo - GnGeo2x
Neo Geo Pocket Color - RACE
Playstation - PSX4GP2X
All of these emulators run most everything full speed, cept for the PC Engine emulator and Playstation emulator.