Reveal your sources! But be sensible, so many "free asset" lists either contain total garbage, or aren't as free as advertised.
Pretty good source. Most stuff is Creative Commons - Attribution, but plenty is public domain.
A little while ago the Graphics Lab at Carnegie Mellon University released all their motion capture data (2605 items or so). Only just discovered this goldmine, can't wait to use it. Someone has been nice enough to convert them all into several popular formats: https://sites.google.com/a/cgspeed.com/cgspeed/motion-capture
Tons of free tilable textures, all free and royalty free.
All sorts of textures. Free and royalty free, as long as it's used in a game or for 3d modelling. Can't be used for open-source projects though.
http://www.iconfinder.com/ and http://www.iconarchive.com/ have a lot of icon style images that are filterable by licence (including commercial with and without attribution) and size.
http://mayang.com/textures/ has a lot of building facades and other misc textures that are free to use.
A Youtube channel I just found called The Music Rack that uploads music licensed under Creative Commons. It mentions which are commercial safe. Has a small but reasonable collection.
Thanks, this stuff is always handy!