There are over 70 breweries in the metro Denver area.
Denver Brewery Guide lists most of them.
Some of my personal favorites are Station 26 Brewing (I work there), Comrade Brewing, Cannonball Creek Brewing, Call To Arms Brewing, Hogshead Brewing (English styles and Cask conditioned pulled with a hand pump) and Yak and Yeti.
There are some fabulous tap rooms that just serve Colorado Brewed Beer: Stapleton Tap House, Colorado Plus (they brew their own and serve about 20 other beers), Alamo Draft House (movie theater with a great bar that serves food and drinks during the films).
There are also some world class bars that offer more than just CO beer but do a very good selection from the home state: Falling Rock Tap House (consistently in the top five beer bars in the country. You can usually find Pliny the Elder on tap along with Superpower from Comrade and Juicy Banger from Station 26. Over 70 beer on tap at any one time.
Beer List, FreshCraft, and Hops and Pie, to just name a few.
Denver IS a beer town. It will be very hard NOT to find a great beer. Most of the breweries are draft only so there is not a lot of trading or national notice. When you get into town be open and try lots of stuff. You will be rewarded.