Just read this and thought I'd pass it on:
"Thai Airways is offering a special pass that entitles travelers to fly to three cities for $169. The three coupons can be utilized to fly economy class to any of THAI's domestic airports during a period of three months. Visitors must book travel by Dec. 31 and must complete all travel by March 31, 2007 and tickets are only available in conjunction with international travel to/from/via Thailand."

that's great....often one way trips are not too much in excess of $50

Does that include all taxes and service fees?

US $149 if you fly with a Star Alliance member.excluding fees and taxes. fantasic deal with the current exchange rate here in the UK

Added to the $169 would be taxes of around $40 ($13 per flight). This makes the cost of each flight about $70. A regular flight Bangkok to Chiang Mai is 2875 baht or $77. Where you really save is on the flight from Chiang Mai to Phuket which normally cost $132

Compare this with the Discovery Airpass from Bangkok Air

http://www.bangkokair.com/discoveryairpass/

You only need to book the first flight date - for any others you just tell them what the destinations are but the dates are open. Plus includes Laos, Cambodia, some Vietnam & China.

The Bangkok Air pass is a little cheaper for domestic flights $50 or $60 plus $12 in taxes (just went up from $9.50) The international fares are $90 plus the new rate of taxes at $17. The pass can be used on Siem Reap and Laos airlines as well.