Amby Duncan-Carr
Prime Factorization: Amby's Resources
What is prime factorization? This site goes through a step-by step process explaining different ways to find the prime factorization.
Wyzant
Wyzant: Prime Factors Calculator
Students input a number to be factored and the WyzAnt calculator does the rest. Limitations include the fact that numbers which are negative or which contain primes bigger than 541 cannot be handled.