When entrepeneur Bill Gates recommends something, most people listen. Bill Gates is using Khan Academy to teach his kids. Khan Academy is a collection of videos explaining everything from addition to statistics, the French Revolution, the Geithner banking crisis plan and Physics. The range is from basic to advanced.
This website would be a great resource for students needing a bit more remediation for a concept that isn't quite clicking yet. Since the material is sequential, it builds upon previous knowledge.
Teachers can use this in the classroom for students who either want to advance more quickly or students who want to reinforce what they've already begun to understand.
Check it out. And see what Bill Gates is recommending!