Founders, of course - GR
Bells of Course - KZ
I am really liking the beers from Greenbush. It's out of the way, but the beer is excellent.
Same with Odd Side Ales. Not right close, but some very interesting beers.
You know what? I'll second The Hideout. It's a very interesting place and the beer is really good. It was once a swimming pool and hot tub party place. Like a club for swinging hot tubbers. Like a sex club with hot tubs... It's a bit sprawling, but very cool and they make some good beer there. I haven't been in like 2 years, so they may have gotten around to remodeling some more since then.
Brewery Vivant for Belgian ales.
There are lots more breweries to choose from. Those are some of the bigger ones. I have also been to Pike 51 in Hudsonville and thought it was pretty nice for a small place. White Flame was pretty good.
I'd like to recommend Perrin, but when we went there the parking lot was more than full, so we just continued on our brewery tour without stopping in. Having had some of their beer at festivals, I can say that the beer is pretty good.
New Holland is a great place to visit as well and they have some awesome beer and spirits, but they are also out of the way. If you can make it, try to get in on a tour on Saturday.