This program is usually $39.95 a school year, but this summer it is free.
"At TenMarks, we believe in student achievement. When students work on TenMarks, they have access to hints and video lessons on EVERY problem, so if they can't recall something, or didn't quite get the topic when it was covered in class, they can quickly review the content, and move forward. Immediate support improves motivation and builds confidence, and our data shows that it does wonders for student outcomes."
I suggest you try it. It seems like a perfect balance between two of my favorites, Khan Academy and ALEKS.com.