Finally, Amazon has gotten with the program and is allowing libraries to loan out ebooks for the Kindle! If your public library subscribes to OverDrive, and you own a Kindle, you're in luck -- you can borrow ebooks for free!
I've been using my library's account to check out books for my Kobo for a while now. Usually I have to place a "hold" and wait a little while, but you can't beat free.
For more info, see School Library Journal's article here.