I found this niffty swap on ravelry, there are just a few more days to sign up if you are interested. They swap knitting books, with yarn for a project in the book. I'm not sure if the intention was to swap stuff out of your own stash or purchase stuff new, but they do have everyone fill out a survey so you know what your partner is interested in.

I signed up, but I think a really cool swap (and if someone has the time to organize it) would be for actual like fiction books etc. You could be paired with someone who has similar tastes and then swap books you have but maybe read once and don't want anymore, and throw in some goodies like a skien of yarn or chocolate as well. I prefer to read new books and once I'm done I'm always wishing I had someone to swap or give them to. For example I tried to pawn of "Beethoven's Hair" to my mom and she's still mad I left it at her house. (after she read it of course) hah.