Every library should have a copy of Wikipedia: The Missing Manual:
I clearly remember thinking, when I ordered my copy of Wikipedia: The Missing Manual, "this has got to be a new low for O'Reilly. How can it be anything but a waste of a ream of paper?" I mean, "Wikipedia: it's an online encyclopedia that anyone can improve". There, what else is there to say? Throw in the URL and you've got ten words. But having read it, pressed it into someone's hands saying "you have to read this!", and ordered a new copy, I can safely say that it doesn't waste any of its 500 pages and is well worth reading.
Wikipedia: The Missing Manual talks about the invisible Wikipedia—the social and technical structures that you only see when you want to contribute. They're what prevent Wikipedia from becoming the other great social literary institution that anyone can contribute to, a public bathroom wall. It gives practical advice on topics like: how to improve articles, how to dispute something, and dealing with vandalism and spam. It even covers the ever-timely topic of deleting articles and "notability".