Sorry if it's already been mentioned, but in all honesty I can't be arsed to go through 4 pages of posts.
www.emuasylum.com
My favourite romsite, what with there being in excess of 75,000 roms/isos there. Admittedly you have to join to get the isos, but not for the thousands and thousands of Nintendo and Sega roms, aswell as a few others too.
(Sorry about sounding like an advertisement for the site, but it's just that damn good!)
Threaded Mode
