DIGAREC, the Digital Games Research Center of the University of Potsdam, published a book about Game Philosophy, that is freely available on the web. The contents are the proceedings of a conference, that was held in May 2008. It covers three topics, that should be relevant to philosophical questions about games: ethics and politics, the action-space of games, and the magic circle. The latter is dealing with the border between games and non-games. The book in total has 344 pages. Direct download pdf.
via A Maze