I want to recommend to anyone looking for a relaxed island experience to go to the Eastern Islands near Trat and Cambodia. We went last February and had a fantastic time without all the chaos that my friends have (happily) reported from the other more often visited chains.
I prefer lounging with curry, eating fish steaks, having a cool bottle of beer and reading a book - for this we found that Ko Maak was wonderful. The food on the bach fantastic and the people were very cool. Ended up spending most of the days listening to the sand crabs chirping - though the water is a little rocky and shallow.
Ko Wai was a great place to relax and hang out with people in the evening.
Ko Chang - KB Bungalows on Kai Bae was affordable and right on a nice coconut grove near the beach. The food at the resort one north (with the deck right next to the water was great).
As well - Long Beach was very secluded and relaxing. Staying at Zion was a great spot at the south end of the Island. We'd come back to this place by taking a fishing boat that was headed from Ko Wai and they just took us up to the beach. Treehouse was a nice place to stay and relax but Zion was closer to the action of the waves. The beach has a great tide effect, becoming massive when its out.
Okay - this was last year and I'm rambling, but I think these Eastern Islands just don't get enough praise.