We just recently had AirWiz (http://www.airwizcleanair.com/) come out – they were on time, professional, cleaned up pretty well and also took photos to show us before and after. I based the decision on good reviews and would definitely recommend them. They’re from suburban MD, I think.
I’d strongly advise against Dapper Ducts (who are DC based). We used them before and apparently they not only failed to clean things, but also left us with the wrong size filter (unbeknownst to us) which left our whole system unprotected and could have caused massive, expensive problems.