There are two helicopter schools that operate out of Jeffco Airport in Broomfield, CO. Broomfield is about 15-20 min NW of downtown Denver. Premier Helicopters operates Robinsons and and Rotors of the Rockies operates Schweizers and a B206. Both are good schools, just be careful on the High DA days in the summer.
Premier Helicopters
http://www.premierheli.com
Rotors of the Rockies
http://www.rotorsoftherockies.com
Hope this helps,
Steve