Wolfram Alpha and Khan Academy will be very helpful in reviewing basic science and math concepts.
In other subject areas, Wolfram Alpha seems like a good source to see information about what info is available elsewhere. For example, I searched Wolfram Alpha for French and found a graph depicting the increasing number of wiki reference articles over time. While this type of data is interesting, the actual content of these wikis would probably be more useful to my search for review in a subject area. It would be much more useful if there were links to specific areas of review in relevant external resources rather than just statistical info about those resources. Wolfram Alpha has a lot of interesting (but not necessarily useful) information. Though I did find that “fractal” allows you to customize your own fractal.

I just wish they could be in color.