http://www.saylor.org/books/

This is something I recently stumbled across on another forum I visit. I haven't yet had a chance to sample these, so I can't vouch for their quality. However, I can say that these are totally legit and might be extremely helpful to someone, whether you're in college, you're taking AP high school classes, or you'd like to learn things without having to smack down $500 for a textbook.

........
*blows the dust off the old mass downloader*