I don't know them all, and don't have time to finish this now, but post below and I'll edit this list to keep them all in one place. (And in no particular order:)
YR:Argentina - Revora's Resource site, and possibly the best.
Project Perfect Mod - Banshee's awesome CNC community(lots of great stuff in the forums)
rami's CNCR - raminator's CNC Resources. Not loads, but good pie. (forum)
MadHQ's Resource Depot - At Zomba Productions, MadHQ's site, loads of good resources.
Sleipnir's Stuff - Forum with plenty to find for those who look.
The Editing Source
Dead Dragon Mods remnants on PPM
Assault Mappacks and Terrain Expansion
C-Gen Backup on Editing Source
Ares Download Mirror
Edited by Nighthawk, 11 August 2010 - 11:03 PM.
CnC Source is not dead, they've just moved their downloads. Also added links for Ares.