Stanford University
Stanford University: Probability Experiment Applets
This site contains interactive probability experiments that allow you to practice concepts such as the Birthday Problem and the Traffic problem.
Cut the Knot
Cut the Knot: Probability Questions
This site defines probability and has a computer-based random number generator. The site has links to more than 100 probability problems which require some prior statistical knowledge to solve, or they can be great "openers" for teachers...