Get Free Books
I happened across this nice blog post by "the frugal panda" (pace, Chris), called "17 Ways to Get Free Books". Of course, to an impoverished but avid reader like myself — with a friendly but not quite adequate public library — this title was like catnip to a cat.
Such fun and a nice summary of some useful resources. Public domain sources, downloadable e-books, and online book exchanges are all here. It may not be an exhaustive list, but it's a nice starting point, certainly. Use it as you like. Mostly I wanted to make a note of it before I lost the link.