Loki showed me this site:
http://www.pixelofink.com/
I always get my free books from there now! They've got a version for Teens and kids too..
Some of them are evil.. they're good books but in series so they give you #1 for free, then you end up spending $3 to buy #2 and #3.. xD
But yeah.. amazon's probably the cheapest place to get books.. I had a look at one of the ebook stores that Sony recommended, and all the books are as expensive as paperbacks and has a horrible browse function...