Emuparadise
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
FreeROMs is another of the fathers of emulation and deal primarily in classic ROMs as well as playstation one ISOs.
CoolROM
CoolROM is one of the oldest ROM sites still on the internet. Big collection but unfortunately no Nintendo ROMs. Their website is translated into many languages.
Roms43
Regularly updated ROM site containing newer consoles such as 3DS, NDS and PSP. Also including a whole list of retro ROMs with multiple download options for each file.
Rom-Freaks
A ROM site with many systems all hosted on an external file host.
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.