Here is a resource for you.
http://www.fermentedlychallenged.com/p/denver-area-breweries-map.html
There are a few newer ones i haven't hit yet that i hear are doing good beer - Mockery & Ratio in the RiNo area specifically.
Breckenridge's main place has moved way south of town, but they still have a brewpub near the ballpark. Here is the summary I usually give out when someone asks:
I would recommend the ones Ive bolded.
These 2 are little out from the others and not easily walked to - I'd Uber or cab if you plan on drinking a bunch.
Crooked Stave sour / brett beers 33rd and Brighton in the Source building
Black Shirt Brewing 37th and walnut
These are 2-3 blocks apart from each other, so easy to grab a beer or 2 at each and head to the next one. The main issue might be getting food at most of these - they mostly do Food Trucks.
Epic 30th and Walnut
Our Mutual Friend 28th and Larimer
River North 24th and blake
Great Divide 22nd and Arapahoe
Blue Moon at the Sandlot 21st and blake part of Coors Field (not sure hours now)
NOT A BREWERY Falling Rock Tap House 50+ taps and food
Jagged Mt 20th and Lawrence
Wynkoop 18th and Wynkoop
These 2 are also apart from the others;
Denver Beer Company 17th and Platte -
Prost 20th and Central (across I-25) - good German style brewery
NOT A BREWERY, but lots of taps and good food. Ale House at Amatos 16th and Central