Re: Glacier National Park
The answers from countr21 are very good.
Personally, I think that you can cover most of what you'll need for fishing in Glacier with an 8'6"-9"0" 5 wt. rod. It's certainly the case for other places in Montana, such as the Paradise Valley area, where you'll find Rainbows, Browns, Cutthroats and Whitefish all in abundance.