I can speak a little about the default renderer in truespace. It is known as Lightworks and for checking your model as you work it is nicely integrated into truespace. It isn't however, in my opinion, a patch on Kerkythea or some of the other free renderers out there. Like Blender, there is a lot of power buried in the truespace gui (which up to V6 I actually like, don't really get the V7 gui). Given that it is free I think it is well worth downloading.

For a while truespace was also a cheap path into vray. They don't offer cheap vray anymore as far as I know but I'm guessing the integration is still there?