http://www.baen.com/library/
Full texts of various Baen books (science fiction and fantasy) available in a variety of formats for zero cost. The catch? You will probably prefer the print copy and decide to buy one. Or, since the available books are the first of a series, you may wish to read the further adventures of, say, Paksenarrian the sheepfarmer's daughter, and will hunt down the remaining books in the series to read what happens. This strategy is not unlike the many free massive multi-player online role-playing games, where the initial game play has no cost but extra features (a horse, for example) will wind up costing you.