Missoula seems to be more of a roadie town. I didn't find a ton of trails, and most of what I found wasn't all that interesting. There is some good fast buff singletrack in an area called Sawmill Gulch off of Rattlesnake Canyon. It's really smooth - you'd be best off riding it on a hardtail. There are a couple climbs and a number of descents; each loop takes about an hour.
Also, a shop disreccomendation. Open Road did some really mediocre wrenching for me. Two days later, I'm tweaking what they did.