Blender 3D. This is the full-monty, and its completely free. This bad boy has an integrated game engine, and more editing tools for 3D than you'll ever need. The game engine it uses is based off of another open-source 3D engine that is fairly easy to edit and script for. (Crystal Space 3D) Using Blender, you can build 3D models, rig-them, animate them, and paint them all within the program itself. Then you can assemble your game logic in the program as well, without doing any low-level coding. I would definitely recommend it, even if all you want to use it for is modeling.