I'm surprised no body has mentioned "Rendergin" : http://www.numenus.de/index_en.html
Its not free however it has some unique features worth paying for : Direct NURBS raytracing and global illumination. This means that you don't have to tessellate your models and therefore their rendered form is not approximated/is perfect.

http://www.youtube.com/watch?v=-gGX1GP_d78

It supports MOI's files directly and scene setup is very simple. The only downside I can see so far(keep in mind its still a beta) is slow rendering speed(when soft shadows/reflections are present) and jumpy interface navigation(seems they are down sampling the image too much).