It's always buggered me (and I have a program that monitors sent uploads) that so many people download from my porn collection but almost nobody downloads any of my books. There is a reason I keep a 700+ collection of books and that is so that people can download them, this might seem pretty pointless but it still vexes me greatly, come on people, humour a guy, download more books.
Actually I have books on pretty much anything from Fantasy to Ninjitsu knife throwing to summoning demons. Yes you read that right, summoning demons, something like that has got to be interesting. I also collect gamebooks so there's bound to be something there to interest even the most die hard of computer players.
So post what rares you have. (books obviously)