I maintain an index to all Babylon 5 3D models available on the Internet. I maintain a second index to sites with unreleased Babylon 5 3D models. Some authors are willing to e-mail copies of the unreleased models if you ask nicely.
The Star Wars Modelling Alliance site has numerous models and images from the movies and derivative works. The models are all 3D Studio meshes, so you will need a converter if you use another modelling program.
The Wolfpack site contains many excellent Star Trek images and a number of meshes for ships from the shows and movies.
B.J. West has created a site with models from the movie 2001.