I just found this website the other day, thanks to Bob at The Daily Blogster.
This archive site has historical documents in PDF. I read a lot of books on history and found a collection of anecdotes compiled after the Civil War, which was very interesting. Teachers could use this site to find resources for their classes. I can't quite believe there's actually 2,555 books, journals, or articles on ants, though!
Check out the education page. There are some great resources to support Advanced Placement courses!