Originally Posted by Rampo

In my experience, give or take a month or two, March-May and late August-November have been the times when I've found the better airfares, although in the last year or so really good airfares have been few and far between. March through May is the hot hot season but Thai New Year (Songkran) which revolves around April 13 can be a lot of fun if you don't mind being soaked to the skin occasionally. (Water throwing is part of the fun.) The temperatures in October and November are more comfortable but may overlap a bit with the rain season.