I find wikipedia quite helpful for getting the basics on a subject, and it works for almost anything, whether it be science, history, religion, or the
latest movie. If you want more detail, however, it's best to move to other sites, books, and the like.
I've got several good sites bookmarked for this sort of thing, I'll list some of the best ones.
Hyperphysics: has a short description of pretty much every physics concept, from the most basic to some of the most advanced
Wolfram's Integrator: I wish I'd found this thing while taking calculus... it can integrate any function, and do it in an instant. The only things
it can't integrate (that I've found) are functions that are just plain non-integrable, like e^(x^2)
WebElements: a periodic table of the elements, with clickable links on each element for more info. Has all from hydrogen to Uuo (element 118)
Crystallinks: some of the stuff on this site is presented from a revisionist point of view, but there's actually a lot of really good history stuff
here, as well as some religion and philosophy and that sort of thing.
Project Gutenberg: THE source for old books whose copyright has expired, both fiction and nonfiction. To comply with legalities, they don't have
anything new, though. I think the law says that books are public domain 75 years after the author dies, but feel free to correct me on that.
Beliefnet: A fairly comprehensive collection of major world religion scriptures, from sources like Christianity, Islam, Judaism, Buddhism, Hinduism,
even the occult.
Depending on what specifically you are interested in, I might be able to give you some more links. I suspect that you're like me, though, and are
interested in a wide variety of different subjects. Have fun!
Oh, two other things to suggest: google books, and p2p sharing. I've used those quite a bit to get books to read as well. Google books only lets
you look at a couple pages from each book, though, for copyright reasons. p2p sharing is illegal in some places, depending on the nature of what you
share or download. Here in Canada, there's no laws against it, but in the US, they've prosecuted a few people for it. I'll let you make the call
on that one.
[edit on 3-6-2006 by DragonsDemesne]