The Loy Krathong Festival or Festival of Light, takes place annually all over Thailand during the 12th full month in the traditional Thai calendar. The main part of the Festival entails the construction of a krathong, a cross between a tray and a raft constructed from trunk of banana trees, which contains a flower, a candle and three incense sticks designed to float down a river or canal. You make a wish as you light the candle and set the krathong afloat. if the candle keeps burning until the krathong is out of sight, your wish will come true. The Festival honours the Water Goddess.

© Hanumann
There are also beauty contest and firework displays. The provisional Loy Krathong Festival dates for 2008 are 11 – 13 November.
October 9th, 2008 on 1:53 pm
I was in Thailand last year for Loy Krathong and stayed in Pattaya at the http://www.canterburytalescafe.com
had a great time and this guesthouse had books on Thailand and its customs etc.
Great place.