I'm late to this party, but I had to chime in.
I have lived (Maryland, Texas, California, Nevada, Wyoming, Utah, Minnesota) and traveled all over the country, and I think Montanans sound most like Minnesotans. The long, rounded /o/ such as in "boat" is very Minnesota-esque, as is the long /a/ sounds in "ag" words such as "flag, bag, wagon," etc. I say "bag" with the same short /a/ sound as in "cat," but most folks around here say "bayg."
Wendy - I'm with you on the annoying Utah accent. I think you ought tuh drive over tuh American Fark to look at the moun'uhns and go tuh some garage sells. Then go getcher trash kicked at Zumba, cuz ohmyheck, it's so much fun! Don't fergitcher Bump-it!