Mathigon
Mathigon: Probability and Discrete Math: What Are Probabilities
This lesson focuses on probability, a number between 0 and 1 which describes the likelihood of a certain event. A probability of 0 means that something is impossible; a probability of 1 means that something is certain.
Richland Community College
Richland Community College: Introduction to Probability
This site from Richland Community College provides an overview of probability including a list of probability rules. Several examples using dice are included.
Other
Utah St. Univ.: Coin Tossing Applet
An interesting Applet that simulates the toss of a coin 100 times. A quick count of the results and an accompanying graph make this site useful for both teacher and student.