EDIT - Gecko is right on the money. Blender is the best.
But
There's another one called Truespace. Microsoft bought the company a few years ago.
Don't anyone colapse. But Microsoft gives it away for free.
Shocking isn't it?
Truespace site http://www.caligari.com/
EDIT2 - Microsoft is discontinuing Truespace support. The download is still available but only for a limited time. Not sure how long. If you would like the program, now's the time to download.