We used Ontario Power Air Duct Cleaning. They were good. I suppose a little pricey (I can't totally remember but for a 2-bed house it was around 400 bucks), but what do I know. They were on Holmes on Holmes and so I figured they'd do a good job. Somewhat surly customer service, but they were professional.
We moved into a house that had undergone major reno, so the ducts were packed with dust. The difference in the air quality was remarkable and the heat was more efficient after as well. I really noticed that.
here's the website: http://www.opadc.com/index.htm
I hope it helps.
I use this website homestars.com and they have reviews of all sorts of companys. You can read peoples reviews of the company and how much they cost for the job etc. Have a look you might be able to find an good company this way.