School Resources
More than a few times I've had teachers at school who do not explain well enough or they make us memorize/study way too much. Many times, I've found other sites or links that definitely helped. I'll update this as I find more. Hopefully this helps out some of you.
General
Wikipedia - If you haven't come across this site by now, you're in for a nice surprise. You simply can't not use this site ever. Basically it is an encyclopedia that anyone can contribute to (but moderated/managed by higher ranked members of course), and it's probably have all the topics you'll ever need from an encyclopedia.
English
Sparknotes - Summaries of books students are commonly required to read.
Works-Cited Format - Near the bottom of the page is a chart that shows almost all ways of citing you'll ever need, including authors, websites, and interviews.
Calculus
Meaning of dx in Derivative and Integrals - Understanding what dx and dy actually mean in Calculus and what you can do to manipulate them; note the method shown is called "Non-Standard Analysis".
Chemistry
AP Chemistry Resources - Practice tests for every chapter in Chemistry, as well as detailed explanations to help your prepare for tests (AP Exam).
Bond Angles and Shapes of Molecules - Very handy reference page for finding the shape and bond angles of a molecule based. Just select the number of atoms surrounding your central atom from the links. It even has drawings and graphics to help with diagrams.
Home-Made Engineering Paper, Front and Back - My chemistry teacher required that homework be done on engineering paper. Sometimes the store sell out since everyone is trying to buy it for homework, or you just don't want to buy it. My teacher accepted printed versions (he thought it was real), so you might also find this useful.
Physics
Physics: An Introduction - Not really an introduction; it actually takes you through 32 chapters and topics, complete with online quizes, practice, and answers. Highly recommended for both regular and AP review.
Newton's Laws Test - Review questions/answers involving Newton's Laws.