Along the eastern coast of peninsular (western) Malaysia is a string of small islands surrounded by coral reefs. With just a couple of exceptions, these islands are clustered at the northern end of the coast, near to the Thai border. Several of the islands have resorts, so the challenge is usually deciding which one to base yourself on. There seem to be only a few liveaboards running around or between the islands.
Not shown on the map is the largest island, Tioman. I visited there in APril of 2009 and have to say the diving is fantastic.