A new 3D Modeling tool has emerged: ShapeShop! It claims:
ShapeShop is a new 3D modeling and design tool with a fun, easy-to-learn interface. Sketch-based shape creation and editing tools make it simple to quickly translate your ideas into a 3D shape, and drag-and-drop decal compositing makes texturing simple. Best of all, ShapeShop is free!
Yep, it's totally free for the taking. However, it doesn't do everything for you. You can only create meshes, which then have to be textured or rendered elsewhere (such as ZBrush, etc.)
Also, 3D Print users should be aware that ShapeShop outputs only OBJ format, not STL, so you'll likely have to do some kind of file conversion. One other item, which may or may not affect you: it works only on Windows XP or Vista.