Learning the Basics
- Wikipedia: Where else would you start?
- Special Relativity - Einstein Online: A good and complete introduction to the topic by the Max Planck Institute.
Other Simulations and Resources
- Space Time Travel: The best all-in-one resource I've come across for visualizing 'seen' relativity
- Real Time Relativity: A downloadable 3D simulator of the effects of relativity.
- Warp: Also has a good downloadable 3D simulator of relativity. In addition, this site has some good, accessible explanations of the effects they show.
- A Slower Speed of Light: Recently released (aka fall of 2012) by a group at MIT, this free downloadable game does a nice job showing off relativity in a 3D world. (Well, 3+1 dimensions, of course). The focus of this game is specifically on the effects due to 'seen' relativity, so the bendy warpy world. It is a quick play, and I encourage you to check it out.