The awesome part of this is that any $10 or less accessory is actually free (no tax or shipping), and includes free 2nd day air. When I mean free, I mean that you do not even have to enter a credit card to purchase these items.
The selection of good items on AT&T for under $10 is pretty slim, but hey! You can complain about the price.
For $2.50 + tax ($2.72 for me) you can buy a 4GB Sandisk Thumb Drive, which is a pretty slick price... (seems to be one of the best deals on the site, besides free phone cases)
$10 off AT&T Accessories