Several books I've read have used anti-gravity as a fictional example of a secret research project, and this made me wonder how much truth there was behind the fiction. In The hunt for Zero Point
Nick Cook examines the evidence for such a project. He details work done in Germany, in particular in secret Nazi laboratories, and explains how this work was transferred to the USA after the war, leading to an anti-gravity 'buzz' in the mid-1950's - which for some reason faded away. Cook goes on to look at how anti-gravity technology might actually be incorporated in current aircraft.
I can't say that I was at all convinced that gravity has been defeated though. Cook is Aviation Editor for Jane's defence weekly and uses this to imply that he has a realistic view of what is going on, but I felt his lack of scientific knowledge seemed to allow him to believe all sorts of technobabble, and to equate secrecy with going beyond published science. On the other hand he does uncover a lot of secret research which has been going on, and if this aspect of the question interests you then you might like to give this book a try.