ATARI 2600 ---> STELLA
NES ---> FCE Ultra
SNES ---> ZSNES
SEGA GENESIS ---> WGENS (Gens for windows)
SEGA CD ---> WGENS
SEGA 32X ---> WGENS
SEGA SATURN ---> nothing yet
SEGA DREAMCAST ---> Chankast
ARCADE ---> MAME
CPS 1 and 2 ---> NEBULA
CPS 3 ---> NEBULA special cps3 version
NEOGEO ---> NEBULA and NeoRage X
Playstation ---> PSX 1.4 and Virtual Game Station (VGS 1.4)
Nintendo 64 ---> Project 64 ver. 1.6 and 1964 ver. 0.9.9
Gameboy ,Gameboy Color, and Gameboy Advance ---> Visual Boy Advance
Playstation 2 ---> PCSX2 Version 0.9.2
those are the best based on my 8 years trials...there other very good emulators for other obscure systems like the Amiga and Jaguar.