As for all our math courses, we have a couple of different options here: the Khan Academy and MIT OpenCourseWare. In MIT's case, we have a set of assignments and exams (all with solutions) to check our knowledge. The Khan Academy doesn't seem to have gotten that far yet, but it may just be a matter of time. You probably don't need me to tell you that you're far more likely to understand a concept if you actually take the time to do the math . . . over and over. Links are provided below.
This is an area I haven't gotten around to studying in much depth yet, but I am starting to see its importance. If you already have some insight on this, by all means share.