Yes, there is a bus. It's number 390, Suvarnabhumi Airport - Talad Rong Kluea.
I can't find the departure times listed anywhere, but at least back in July 2008 there was one around 8 am which I took, and another one later (around midday?).
not sure if website is up to date:
anyway there's a phone no. there that you could call (or get someone to help you call) to confirm.