SPACETIME WRINKLES. Wonderful images and movies about gravity waves and the interactions of black holes. The movies are worth the wait to download.
C-ship: Relativistic ray traced images.
Explore the consequences of relativity in a ship traveling at light speed c.
Relativity and FTL Travel.
Relativity theory for the Star Trek fan.
There's some nice stuff and anyone in this class should be able to get something out of it. There are some further insights than I had time to consider in class.
CLAUSTROPHOBIC PHYSICS: An
introduction to the theory of relativity and
Poincaré Symmetry.
This requires a bit of calculus.
Welcome to Tensors and Relativity 1997.
This site requires more than calculus, though someone with a little DE under his/her belt could get something out of it. The author says: "This course aims to provide a basic introduction to General Relativity and the
mathematics necessary for an understanding of the theory. I hope you will all
enjoy it as much as I did when I first took the subject ten years ago."
Check it out if you're interested in seeing the type of mathematics that you would see in relativity theory.