Marilyn Vos Savant's Monty Hall Problem: Simulator. Uses buttons as labels and controls. Counts tries and provides percentages. Can be Reset without page refresh.
Mathnet : The Car and the Goats: Introduction to the problem and the controversy. As well as a simulator. Contains a link to the next page which explains the maths behind the problem.
Monty Hall: Contains a introduction to the problem, a hint to the solution and the solution. The author attempts to "provide a reasonable and clear explanation of the answer".
Monty Hall Dilemma: Includes the original question posed to Marylin vos Savant about the problem, a simulator, solutions and other information on the problem.