I've just spent a few days on Koh Chang on the S.E. coast of Thailand. It was the first time I'd been there, and I must say it was really idyllic, much less developed than Phuket or even Koh Samui. In fact, it's rather like Koh Samui was about ten years ago.
There are some important differences, though. The main one is the hilly nature of the place. It makes for some really spectacular views, but also some pretty hair-raising experiences if you're on a motorbike! Also the beaches aren't quite as good as those on the more reknowned islands. Mind you, this is compensated for by the dense jungle interior and some fine waterfalls.
Vacationing back in the U.K. now before stopping-over in Cairo on the way back.