THE SUCCESS OF OPEN SOURCE – Steven Weber (methodology of open source, not just software and great historical overview)
Harvard University Press
ISBN 0-674-01292-5

open sources 2.0 – THE CONTINUING EVOLUTION (collection of articles and papers edited by Chris DiBona, Danese Cooper, Mark Stone)
O'REILLY
ISBN 0-596-00802-3

producing open source software – Karl Fogel
O'REILLY
ISBN 0-596-00759-0

Understanding OPEN SOURCE & FREE SOFTWARE LICENSING – Andrew M St Laurent
O'REILLY
ISBN 0-596-00581-4