The emulators ive gotten to work best so far are:
Project 64(N64 emulator)
Visual Boy Advance(GBA/GBC/GB emulator)
There are also a few others ive tried, but dont use as often, they are:
SNES9x(SNES emulator). Havent used this one as much, but it seems to run fine
NullDC(Dreamcast emulator). Also havent used this as much. Only tried running one game on it, and it worked fine, so it seems to be ok, but im not 100% on it
Dolphin(Gamecube/Wii emulator). So far ive only gotten one game to work on it, but that could also be the fault of some of the roms ive tried. Still though, im pretty sure it cant run most games, i think its still being worked on actually, but im not holding my breath for this one. Kinda sad though, since the Gamecube days are finally dying out, i was looking forward to Gamecube emulation.