If you like working with 3D animation or scenes, you should stop by the NASA 3D Resources site. They have a number of 3D models there free for public downloading and use, including the Shuttle, the ISS, and the Hubble Space Telescope. Another good resource is SciFi Meshes, where a community of model builders upload and share their work. 3D Total has a number of free models and textures, as well as a series of tutorials for creating your own.
