An interesting review of DARPA projects (2 volumes), "Transformation and Transition: DARPA’s Role in Fostering an Emerging Revolution in Military Affairs":
http://www.darpa.mil/WorkArea/DownloadAsset.aspx?id=2686
http://www.darpa.mil/WorkArea/DownloadAsset.aspx?id=2687
Stealth, PGMs, UAVs...