There are currency exchange booths at Suvarnabhumi Airport from the banks, but, as you may know, usually these booths do not give you good rates like exchanging money at the branches of the banks in town. Anyway, if you have to exchange money at Suvarnabhumi Airport, here are the recommended booths that would give you better rates than the booths from the banks: SuperRich (Orange), Value Plus Suvarnabhumi, and Yenjit Exchange.
All three booths are located Near Airport Rail Link, B floor, Suvarnabhumi Airport Terminal. They have different opening hours. You can either check the exchange rate at their websites, or walk around to see and then choose the one that gives you the best rate.
Update: January, 2015
Opening hours: Everyday from 10.00-20.00
Value Plus Suvarnabhumi
Opening hours: Everyday from 6.00-23.30
Opening hours: Everyday from 10.00-18.00
Update: June, 2016
And if you are in Bangkok, the list of the shops that give you the better rate than at the banks can be found here. Hope this information helps!
Have you ever exchanged money at these two booths at Suvarnabhumi Airport? Did you get a better rate? Share your experience with me in the comment!