The Duct Man just completed a two day whole house vent cleaning. It was actually more than vent cleaning. He cleaned the attic air handler coils and sealed the entire system. I just had two condensers installed and he fixed what the air conditioning service rep missed. He thoroughly cleaned 17 vents and sealed them with an anti-microbial agent. He meticulously checked each part of the air conditioning/heating system. He was also careful to keep the area where he was working covered and cleaned up after himself routinely. He's not the cheapest, because he doesn't do the standard "bait-and-switch" offers. He is a professional duct system technician; he has the special equipment and knowledge to do the job properly. He quoted a price and completed the work on schedule for the amount he quoted. This is certainly one of the cases where, "you-get-what-you-pay-for." He also cleaned our dryer vent and was as thorough with that as the others. We won't be due for another cleaning for 8-10 years.
I highly recommend "The Duct Man."