Library of 3D scans of artifacts from the Smithsonian Museum. Many of the files are free to download for printing.
Tinkercad
A basic, but powerful CAD drawing application. Emphasizes precision over organic sculpture. The web based software is easy to use and is good for precise shapes and mechanical objects.
With Tinkerplay users can easily design and 3D print characters, or anything else they can imagine using the built-in part library. Users drag and drop parts together.