In reply to Nic:
There's a tiny bit on Koh Pangnan that's documented but its not far to Koh Tao which is a mecca for bouldering, and there's a good bit of sport climbing (and a tiny bit of trad, but loads of potential). I worked there for about a year and we bolted loads of routes including the islands first (small) multipitch. Check out goodtime adventures as they have a free downloadable topo map.
If you can't make it there, I'd still bring your shoes and chalk bag as all three islands are granite and there's bound to be a bit of exposed rock on Samui if you explore far enough away from the main centres.