Capital of the province that bears its name, Trang is not a must see in itself, but, with a bit of effort, can be fun.
Nai Yang is a large beach on the northwest coast of Phuket. 
Haad Yao is a white sand beach on the north of the island of Koh Phangan. 
Khao Sok is a national park north of Phang Nga Bay, not far from the tourist island of Phuket. 
Ayutthaya was the second historic capital of Thailand, then known as the Kingdome of Siam. The city was founded in 1350 and today still houses the remains of ancient temples.
Situated on the Thai border, Chiang Khong is essentially just a stopping off point for travelers who are going to Laos (or vice versa).
Bangkok is the capital of Thailand. Once a small commercial town on the banks of the Chao Phraya river, nowadays the town has more than 8 million inhabitants, and is the symbol of the country's economic development.
Chiang Rai is a town perched in the mountains in the northern part of the country, near the border between Laos and Myanmar and the famous Golden Triangle.