Recently visited this site (http://xkcd.com/832/), sent to me by a friend of mine, that provide the optimal moves for Tic-Tac-Toe. It is actually the “Complete Map of Optimal Tic-Tac-Toe Moves” that help you never to loose in a Tic-Tac-Toe anymore!
(click on the image to view full size image, the image taken from http://xkcd.com/832/)
Have a try!