If you downsized your unread book collection via paperbackswap, and find yourself with a lot of credits but nothing to order, you can donate unused credits to schools.

(If you have not joined, the idea is that you list your books on the site. Other people can then request them from you. When they receive them, you get a credit. This credit can be used to request another book. You only pay the cost to ship YOUR book. There are many such sites now, but I find paperbackswap to have the biggest selection of the kinds of books I read (fairly eclectic). You can join by clicking here. If you list 10 books, you get 2 free credits without having to send anything yet.)