Good guide book: An Angler's Guide to Montana. Find it at Amazon.
My favorite if you get there before the runoff is the Big Hole. Easy river to run. Go to Wisdom for shuttle info. Best lures are Rapalas and Big Super Dupers. Best flies are The Kauffman Stone and the B-itch Creek. Get it in the willows for the browns during high water.One day a couple of years ago, I caught Cutts, Bows, Browns, Brooks, Whitefish and Grayling, all on a Bead Thorax Pheasant Tail

Beaverhead is also a great river in the area, but a boat is very important. There is a low Highway bridge that can cause headaches to drifters, ask around in Dillon.

Couple of other good bets if you wanna drive are the Mussleshell, and if the runoff is late, the Yellowstone, Paradise Valley, especialy if you got a boat. Some nice zippers drain into the Yellowstone from the mountains to the east.