I recommend trying the Kettlehouse Brewery. There are two locations in town and both serve pints. Check online or phone book for address/directions. From my experience it is the most favored by locals of the three. For sheer variety, you might also try the Rhino tavern on the corner of Ryman and Front Streets downtown. They have I believe 50 taps (much of it regional craft brew) even though it's a dive, and good prices. Worth a visit! There's also a fun Irish tavern/restaurant 1/2 block off of Higgins on Pine Street, called Sean Kelly's.
I feel the best I can do is steer you to places with great beer and atmosphere - you'll have to use BSP ("Beer Sensory Perception") to find a style and good example of it suited to yoru tastes, or ask the bartender for recommendations. I moved away too long ago to mention brews by name and you never really know what is the flavor of the month. FWIW, I used to favor Blackfoot IPA amongst the MT IPA's. There are lots of great beers to try in Missoula!
Also, two good stores to buy craft beer by bomber or 6-pack, Worden's (downtown near the end of Higgins Ave - also sells 12 oz. singles), and for prices the Orange Street Food Farm at Orange and S 5th E.