ShapeOnYou is a 3D tool for drawing and rendering basic 3D objects that can play nicely with other 3D-friendly applications like Keynote and OmniGraffle 4. It features an iWork-like inspector to give you an intuitive interface right out of the box, and it comes with over 20 shapes, as well as the ability to create your own. ShapeOnYou also supports the LinkBack framework, so if you embed a ShapeOnYou project in other LinkBack-enabled apps (such as Nisus Writer Express, Curio, OmniGraffle, OmniOutliner and more), the object will be updated in those apps if you make any changes from within ShapeOnYou (a genius framework, really). Finally, ShapeOnYou can export to a wide variety of formats such as PDF, EPS, SVG, VRML, X3D, TIFF, PNG and JPEG.
However, since I'm really not that versed in the realm of 3D, I'll stop pretending and just let you check ShapeOnYou out for yourself. ShapeOnYou is a Universal Binary and is available as donationware here.