The website reviewed this week was Loci, an online publication of MathDL/MAA. The review mentions the department Resources, which offers free learning materials on diverse mathematical topics, each having been classroom tested and peer reviewed.
An example is the activity Probability Aquarium, written by Melissa Jackson and Kady Schneiter at Utah State University. The main component is a Java applet that "presents basic probability rules in the context of interactive questions based on selecting fish at random from an aquarium."
Eight different situations or questions are posed, with increasing complexity. Using the context of an experiement, the key mathematical ideas are determining probabilities based on sampling with or without replacement.
To help an teacher, the activity includes a recap of the instructions and poses questions for monitoring student understanding.
Ask your students to try it, regardless of their mathematical level since the program guides their investigation. And if you dare, test your own understanding of determining probabilities based on sampling with or without replacement. I know, you say you "probably will!"