Delicious (http://delicious.com/) is already one of my new favorite sites. I love how easy it is to use and organize. It would be great to create a school account with a list of all of the great student sites or teacher sites. Then students or teachers could log on and do a search for what type of information they need and the sites would be listed. Other teachers could add to the list and it would be a wonderful collective resource for everyone.
Lulu (http://www.lulu.com/) is also a great site. This would be a great tool to use for school fundraisers by selling class or school created books. It is also great for aspiring writers to 'publish' their own books.
Biblio (http://www.biblio.com/) is a great alternative to amazon. Although I love Amazon it is often hard to find used & out of print books. This would be a great site to use for text books, collectors books or just for cheaper prices in some cases.