I gotta say Dillon Dam Brewery in Dillon, CO, but only because they are going to start selling me grains and hops at their cost.

(I don't have any LHBS)
I am amazed by all the Breckenridge love in this thread. Their small batches are very good (471 IPA, Pandora's Bock, ESB), but they often only have 1 small batch available in Breck. I don't know about Denver; probably more. I eat there a few times per month, and I'm often unimpressed by the beer. Vanilla Porter? Disgusting. WAY too much nilla.
I would say my favorite is Great Lakes Brewing company, since Edmund Fitzgerald is the best robust porter ever made by mortal men. However, now that I live in CO, I AM living without them.
If I could never have a different BC's beer, it's gotta be Avery. The Maharaja, Dugana, Mephistopheles, The Beast, Brabont, etc etc etc
Some more than worthy runners up:
Boulevard - only had a few, but they were all great
Russian River - plenty to love there
Deschutes - Black Butte (2nd favorite robust porter)
Great Divide - Yetti Espresso Imperial Stout WOW!
Oskar Blues - Ol Chub yay!!
Not so micro:
Stone - tons
Rogue - Had the Double Bastard. whoahoho that's some good chit
Dogfishhead - I rarely get them, but the Palo Santo Maron is amazing, all are very good, and I usually have a few of theirs in my cellar
Edit: Had to remove Goose Island - I can't live without the occasional Bourbon County Bourbon Barrel-Aged Imperial Stout, but that's the only one I've been able to get.