This well-written explanation of relativity includes animations and pictures which may be helpful in understanding a tough topic.

This site from the Georgia State University provides an interesting chart form of the ideas of relativity. Column 1 - Idea, Column 2 - Experiment. Each item is linked to its own page of explanation, which is well done. A nice type of...

At this site from the Georgia State University is where the proof all starts. One must understand this experiment to have any confidence in relativity. Here's the experimental setup and a summary of the data.