Mtnboomer
Can't argue with any of the flies suggested … however you might want to take a gander at Caylorscustomflies.com . I've purchased flies from him in the past and he ties all the attractors , nymph, streamers you'd need for Big Sky FFing- plus they're tied here in the USofA and he can custom tie whatever else you might want . I live near Bozeman and avoid crowded places like the Madison , mostly fishing smaller freestones - and depending on when you come out here don't forget about the backcountry lakes they can be very good in the spring when creek/rivers are blown out . My personal fav's for creeks and such : Royal-basically any of the Trude style flies- size ten when the water's up, 16's later, they make a good caddis imitation in smaller sizes AND they can be swung downstream like a wet fly- especially when there are Brookies around . 'nother fly you might try is called the Purple Haze - basically a violet shade of a Parachute Adams works well especially towards evening when light gets dimmer . Stimulators, Elk hair caddis, House and Lot Turcks Tarantula- good one when the water is rough . Good luck and tight lines-
Tortoise