Ayam a 3D modelling program which seems to use Renderman as the rendering engine. Uses TCL for extensions, and seems to have a basic Motif-style interface.
K-3D seems to have the nicest interface (based on the screenshots). May be somewhat early-stage. Depends on external rendering programs, such as yafray (a ray-tracer) or aqsis (a RenderMan clone), and if one isn't present, and you ask for a preview, you can spawn a bazillion viewer windows.
Art Of Illusion, a Java-based app which is rather easy to use (since I learned on Lightwave, and this seems pretty similar). We have a local copy of its manual.
Moonlight 3D used to be QT-based, now seems to have switched to Java. Couldn't get to run on my machine.
Wings 3D, a modelling-only program.
An overview of Linux 3d apps, including modeling programs, rendering software, even CAD software.
