EmuParadise.me - A giant collection of emulators and roms. One of the best!
CoolRom - A Rom collection with only working dumps. Great for quickly finding known roms.
ROM
Collector - A cool site where you can purchase ROM sets on CD for a
nominal fee, mailed directly to you. Very cool for the avid collectors
out there.
GameBoy Advance ROMs - This site specializes
in GBA ROMs. They have anything and everything related to GameBoy
Advance.
ROMNation - Probably the 2nd most comprehensive,
easy to use, BIG romsite on the 'net. Thousands and thousands of games
for dozens of popular systems. Top-notch quality emulation.
TheROMs.com
- Thousands of ROMs, hundreds of emulators, zero BS.
RomCenter - Audit and repair your roms with
this program. Site also hosts hundreds of games available for
download.