Originally Posted by GoingAway
Only thing is to make sure you don't get only large bills as the taxis can't always break them.
Could break it at the hotel front desk while the cab is waiting outside
Really, you only need enough baht for the cab ride to the hotel and a little bit so use the automatic money changer (at baggage claim) and change like $20 (THB800) or thereabouts, and then use your ATM thereafter. ATMs are everywhere in Bangkok.