Personally I thought Pattaya was a hell hole. There are an absurd amount of hookers there, to the point that it's tough to walk down the street. (I suppose that could be viewed as good or bad, but even if you want hookers, you don't need 50k of them
)
In the south, yeah, check out the islands man... I liked Phuket also, but I'm not sure whats left of it since the tsunami.
If you can get up north, Chaing Mai is a neat town. Small, but cool history, and you can make it out to a hill tribe on a motorbike pretty quickly.
Man I need to get back there.