Here are some links for you:
http://www.openrm.org/ <---scene graph management library (free)
http://cal3d.sourceforge.net/ <---skeletal animation library (free)
http://www.libpng.org/ <---PNG compression library (free)
http://www.zlib.org/ <---compression library (you guessed it, free)
BTW,
http://genecys.sourceforge.net/ was made with a bunch of free libraries, check out some of them on the bottom.