I visited early on in my birding career and as part of a bachelor party, where birding was not the main priority, but Glacier National Park was maybe the most beautiful place I've ever been. Without really knowing what I was doing, or looking up nearby Hotspots, I found some good birds, including lazuli bunting, red crossbill, bald and golden eagles, and a spruce grouse right in the middle of the hiking trail. Grizzly bear, moose, bighorn sheep and mountain goat as well. I'm sure if you head to east Montana, you could find some of our declining grassland birds like longspurs, Sprague's pipit and maybe some grouse species.