Probabaly Bryce or 3d Studio Max. Those are two great 3d render programs out there. Oh and there is Maya, another professional render device.
but of course there is a free alternative. Its called blender. its opensource so you can further the cause if u know how 2 program. You can make renders, animations, and 3d games in it. its great. I am trying to learn how to use it now so I can start making 3d renders soon.