The best fishing in Colorado is Eleven Mile Reservoir (if you like lakes) and the river just above and below the reservoir. Those stretches of river are known as the "Dream Stream" above the reservoir and "Eleven Mile Canyon" below the reservoir. The fishing is not as good closer to Denver. Fishing holes closer to the cities get a lot of pressure.
11 Mile Marina gives great fishing advice.
http://www.11milesports.com/
The best Colorado fishing forum is here:
http://www.fishexplorer.com/co/fxrforum.asp
But they are not as open with the advice as folks on Salty Cajun.
July is very beautiful in Colorado, but May, June, and September are the best fishing months. We've had many trips in June where we've boated 20-30 fish an hour.