These are links to some sites like Westwood and Xcc utilities. (As a note, XCC is down and I haven't been able to find it lately)

Westwood, creator of all C&C games
These below are all mod sites. I have submitted my mod to most (if not all), of them.
RA2 mod makers, lots of modding stuff
Red Alert2 Xtreme, more modding stuff
Raden, an excellent general RA2 site.
Red 2 World, 5.
RA2 Experience
RA2 Map Depot, mostly maps, but some mod stuff.
XCC mirror site.
SergeantMacsCorner
RA2 Communications Central, second to have my mod.
RA2.net, not a bad site.
Tiberium MW, has info on ALL C&C games.
XRA2X, first site to have my mod. I owe a lot to them and I'm not afraid to say so.

These sites are dead/and or dying and/or just plain suck now
RA2 Factory, with lots of stuff that helped me out, just plain sucks now. Look at the "news"