Blender
Blender is the perfect all-in one 3D modelling software. Get all the bells and whistles of a commercial animation and modeling software for ZERO dollars. Yes, as unbelievable as it sounds, Blender is an open source software under the GNU Public License.
It has become the first choice software for even professional animators and has spawned great animation films as well. Films like Big Buck Bunny and the upcoming film, Sintel, was created from this groundbreaking software.