RetroArch - RetroArch is a frontend for emulators, game engines and media players.
Romulation - Romulation provides information and downloads for classic game system emulators.
mGBA - mGBA is an open source emulator of the Game Boy Advance. The goals are speed and accuracy.
FreeROMS - FreeROMS have been giving a tremendous choice of ROMS and emulators to game fans for a considerable length of time.
DeSmuME - DeSmuME is a freeware emulator for the NDS roms & Nintendo DS Lite games created by YopYop156.
Roms Mania - A working online resource for roms.