3D Total - Free texture library.
Animation Buffet - Free rigs.
AnimReference - Animation reference videos for human and animal motion.
CG Student Awards - Award winning student work, great to see what others in your field are doing.
CG Textures - Texture library, free to sign up for an account then you get a specific amount of Mb downloads per day.
Footage Crate - Royalty free Video FX including muzzle flashes, fire, explosions, dust, smoke, backgrounds, and more.
Free Sound - Free to sign up for an account and download sound clips.
Sounds Crate - Royalty free sound effects and music.
Reference!Reference! - Animation reference videos for human and animal motion.
Texture Mate - Free textures, brushes, patterns, and design articles.
Texture Max - Free high resolution textures and reference photographs.
Texture Lib - Free texture library.
CG Trader - Free 3D Models
Free HDR Maps: HDRMaps, HDRLabs, HDRI-Hub