To add a few more to the mix--look at Robert Taber's The War of the Flea, the reprint of the 1940 USMC Small Wars Manual, and its descendant, FM 3-24 (Counterinsurgency), released in December 2006 and now available commercially. You might also want to hunt down a copy of Roger Trinquier's "Modern Warfare," based on his experience in Algeria. Finally, check the October 2006 edition of Military Review, which was a special edition "Counterinsurgency Reader."

Hope this helps.