I often go to the Library Discard sales. They have them about every 6 months or so. I've got heaps of books here for 10-20 cents (Australian) - depends on who's adding up and how well they know me. Of course, they're not in pristine condition but they're great for books that you might just enjoy and not really absolutely love.
I also picked up A Game of Thrones for $2 from a cheapie table at a bookstore and didn't realize at the time what a treat I was in for - and what a bargain I'd got.