Free Daily e-Books (customized to your likes)
I used to belong to bookmooch and I loved trading books. There was also the chance that the book would not make it to me or to the person I sent it. Which I find really odd. The difference between Media Mail and other mail is, about 25% of the time you will not get your items via media mail.
Anywho, this site does it digitally so I don't have to worry about the media mail issue.
You can also post an author, a free book or one for sale. I have only put books foe free on Smashwords so I can't say for sure what the platform is like to post your book. BTW, I highly recommend Smashwords to for anyone looking to publish. You get a free ISBN! Love that!