There's a book by Nick Cook, who works for Jane's Defence Weekly, called "The Hunt For Zero Point - One Man's Journey To Discover The Biggest Secret Since The Invention Of The Atom Bomb" which is all about anti gravity.
Basically he tries to find out if the US government actually cracked this years ago and have since covered it all up. It's quite interesting and pretty convincing, but maybe I'm just gullible!!! It's well worth a read anyway.