Went to open a Bangkok Bank account yesterday as I want the easier/cheaper option for transferring money from the US.
As others have suggested, I went to the branch on second road opposite Soi 6. Not being familiar with that part of town (honest), I got off the baht bus when I saw the sign for Soi 6/1 and wondered a few meters in the wrong direction before turning around and spotting a sign with the bank logo.
The banK has blessedly strong AC. I'm surprised the staff weren't wearing sweaters.
Bangkok Bank's website has a page on opening accounts. http://www.bangkokbank.com/Bangko