Well, of course I have to plug my own site first.

http://www.abandonware.whitesqrl.com

Then there's these.
Arnold's C64 Archive
C64 Unlimited
http://www.planetemu.net/
Quality Roms
Planetemu
Arcade Abyss
Cherry Roms
World of Spectrum
SpekSNK
EmuSNES
MAME Fans
Nostalgia
SMSRen
Haggar's Public Domain
The Old Computer
TZX Vault
Cadeaux
Paladinken's PC Engine
PCEngine Bible
EmulaFox
One Minute Left Emulation
Magyar C64 H.Q.
Arnold's C64 Archive C64 Unlimited

A+ Certified PC Tech Guy/Seitentaisei