If you're a college student with a valid .edu email address, you can sign up for Amazon Student, which gives you Amazon Prime free for 1 year.
$79 value
Unlimited free 2-day shipping on textbooks and millions of other items
No minimum order size
Upgrade to 1-day shipping for $3.99/item
While I guess anyone with a .edu address can try to sign up and use Amazon Student (some schools, like Georgia Tech, have "email for life" programs), the Terms & Conditions say that you must be enrolled in a U.S. college and must be able to provide proof of enrollment at any time. Failure to do so may make Amazon require you to reimburse them for any benefits you may have received.
Oops...I just saw txpacer's similar thread in the Academics forum. I think Chit Chat may be a more frequently visited forum and thus may reach more potential Amazon Student beneficiaries, but I wanted to give credit to txpacer for posting this news first.
This only applies to purchases shipped from Amazon warehouses, and not to third party vendors. Other than that, it is a fantastic deal. Won't cover shipment of either my son's or my textbooks.