Amazon is offering a free 6-month Prime Membership to students with a valid .edu email address. This entitles you to free 2-day shipping no matter how small your purchase is. You will also get free release-date delivery on video games, books and more.
You will also get a free $3 MP3 credit when you join Amazon Student (free.) Nice! I would imagine teachers would also be able to sign up for this one as long as you have a .edu email address. You can go here to get started.