Emuparadise is without a doubt one of the oldest and biggest emulation websites. While they have ROMs they also focus on game guides, game sountracks and related videos.
FreeROMs is another of the fathers of emulation and deal primarily in classic ROMs as well as playstation one ISOs.
Rom Hustler
A regularly updated site with all classic systems as well as Mame, GameCube and Playstation 2!
Sony ISOs
A site dedicated to ISOs for all the major Sony consoles and handhelds.