1 Ko Samui
One of the largest islands in the gulf, Ko Samui is known for palm-fringed sandy beaches, coral reefs and coconut trees. While there are many high-end resorts on offer, there is also plenty of wellpriced backpackers' accommodation.
You can also eat cheaply at street food stalls around the island. For a less touristy experience, head to the southern or western sides of Samui, where descendants of the original Chinese settlers reside.
2 Ko Pha Ngan
In the southeast of Thailand, this island is best known for its monthly Full Moon Party, an all-night affair that draws thousands of visitors.
Most of the parties are centred on Sunrise Beach in Haad Rin, where bungalows cater to the backpacking crowd. The interior of the island contains beautiful waterfalls and lookouts that are well worth a hike.
3 Ko Tao
This is one of the smaller Thai Islands at approximately 21sq km. It's popular as a diving location, with a variety of dive sites and shops to choose from.
Shark Bay is good spot for a day's snorkelling excursion - and the sharks the beach is named after are just small blacktip reef sharks. Other popular beaches include Freedom Beach, Laem Thian and Mango Bay.
4 Ko Lanta
Off the Andaman Coast of Southern Thailand, Ko Lanta consists of several islands - the two largest being Ko Lanta Noi (Small Lanta Island) and Ko Lanta Yai (Big Lanta Island). The bigger island is where most of the action takes place.
While it was originally popular with the backpacking crowd, the island has expanded to have more mid-range to luxury accommodation on offer. Largely flat, Ko Lanta has miles of beautiful beaches to relax on.
5 Ko Samet
Get away from the crazy bustle of Bangkok on this island, which is mostly a national park. It's known for its beautiful white sand beaches and there's a range of accommodation available.
Beaches such as Ao Noina, Ao Phutsa, Au Nuan, and Ao Wai are best if you're looking to relax, while those looking for busier spots with more activities should try Haad Sai Kaew and Ao Hin Khok.