3D Forums
3D Commune - A mid-sized site with forums and downloads for the most popular hobbyist art software programs.
Animotions - This is the place for anime and comics themed needs.
CG Talk - This forum tends towards higher-end programs and has industry news, etc.
Poser Pros - Dedicated to Poser, this site is more focused on techniques, but does offer some downloads as well.
Renderosity - Downloads, Tutorials, Forums, everything you could ask for is there. (Warning, I'm biased. I'm a moderator there.)
RuntimeDNA - Founded by two well known 3D artists, this forum is rapidly growing.