Koh Chang in Trat province is the last of Thailand's big islands to be developed into the "next Phuket". It's the "last" quite literally, as the island sits just off the coast of Cambodia. Koh Chang is about as far east as you can go along the coast and still be in Thailand.
Not long ago, Koh Samet in Rayong provinces was a place just for campers, with just a few rudimentary bungalows, but like most other islands in Thailand, there's been a gradual introduction of more up-scale places. Samet is still pretty much a place for the young at heart, but at least you can sleep in a nice air conditioned bungalow after a night of partying.
Just off the mainland at the southern end of Krabi province are the two large islands of Lanta Noi ('Little Lanta') and Lanta Yai ('Big Lanta'). The two big islands are at the center of a group of 52 islands, 15 of which have been designated as the Koh Lanta National Marine Park.
The Phi Phi islands lie near the mouth of Phang Nga bay at about an equal distance from Phuket and Krabi towns. Although technically part of a national park, the islands have been developed almost as long as Phuket.
Phuket is Thailand's largest island, a idyllic site for the country's premier international beach resort. Much of the island's charm is that the ocean facing west coast is lined with a series of bays where white sand beaches span between two rocky points.
Samui is the largest of about 80 islands lying off Surat Thani province. Tourists started visiting here in the early 1970s and the place started to gain popularity among the backpacker set as Phuket's rising number of visitors started making it too expensive.