If you are looking for a place on the net that will help you refresh your knowledge in mathematics, you should check out KhanAcademy.org.

Simply by accident I found this site that is not only a wonderful resource for learning math (for free) by doing exercises online but also contains loads of video lessons covering physics, history, art and much more. My first contact was a video lesson I found on youtube on properties of frequencies. The videos provided by Khan all follow the same beautiful style. Black screen, color pencils and the voice of Salman Khan, the guy behind Khan Academy. You should give one of his videos a try. I was simply impressed by his clarity.

I have been using the service for more than two months now and I’m still surprised about how well things are explained (especially when it comes to topics like quadratic equations and similar).