Game Center - Game Center brings social gaming to OS X and iOS apps.
Roms Mania - A working online resource for roms.
GameStreamer - Connection people and games anywhere.
ROMNation - Rom download site
OpenGameArt.org - A site dedicated to sharing artwork & other assets for game development.
RomsGet - Download Free ROMs for NES, SNES, GBA, N64, PSX, PS2, PSP, XBOX, GAMECUBE, WII, NDS and more! Works with Windows, Mac, Linux and Android.