I am a massage fiend. I love them. They are one of the reasons that I love Thailand. I struggled to find good information on places to go and accordingly, I would like to recommend the following:
Lampan Massage - Just off Khoa Lak town main street down a side street on the same side as Creative Tailors (which after extensive research and items made, I also recommend.) Next door to the 'AK-47 Bar'. Excellent massage, clean beautiful traditional setting. Highly recommended. Phone: 089 931 5088 Price at at Aug '12: 300B for a tradition Thai massage.
I went to a few places and there are one or two other places that I would also recommend, but have to look for the details at home!