Some links for CFS3 and FS9
http://www.sim-outhouse.com/
Very good forums for all flight sims - lots of downloads etc
http://www.avhistory.org/
Good site for downloading new CFS aircraft
http://www.simhq.com/
Recently discovered this one, but it looks good
http://www.netwings.org/
Good downloads for CFS, IL2, and FS - good forum too
http://www.simviation.com/menu.html
Good downloads for the FS series