Sorry, but which topics in particular do you find lacking on Wikipedia or mathworld, for example?
The math and physics articles are generally pretty good, include derivations, background on the subject, and you can then click to learn about the personalities who discovered the idea. There are no problem sets, however.
This is one problem, the other problem is that there isn't a good way to sort the articles by prerequisites. There's also no easy way find out what you don't know you don't know about a subject.
