Blender has a steep learning curve, but you definitely can't argue with the results. I come from a 3dsmax school of thought so the first time I used it I was confused and frightened, but once you get used to it (I'm still not) you can pull some amazing visuals out of it. If you're going for prerendered graphics you want to avoid the "prerendered look" as much as possible, which imo excludes a lot of the less developed free 3d apps out there.
If you're going to be rendering out to 2d images and not distributing any native format files, I might also gingerly suggest that just because a program is sold commercially doesn't mean it couldn't be a 'free' solution :p