So far there are four full length novels. In order they are: Odd Thomas, Forever Odd, Brother Odd, and Odd Hours. There are also two manga style stories that take place before the events in the first novel. They are Odd is On Our Side and In Odd We Trust. There are more Odd Thomas novels to come and another manga called House of Odd is to be released on March 20, 2012. I hope this helps. Enjoy!
Yeah, I'm eagerly anticipating Odd Apocalypse to be released on July 31, 2012 which will continue the series after Odd Hours. Right now I've just started reading 77 Shadow Street which is pretty creepy in the opening chapters so far.