Iverson Snow shoes, Marble Arms, Northern Mist Longbows, G Fred Asbell, Keweenaw Brewing Company, Bells Brewing, Fred Bear and many more I can't think of right now.
I will absolutely second bell's oberon, that is the definition of summer beer. And I know it's not totally unique to Michigan, but the mid west, I'm going to throw culver's out there, because that place is just awesome