My favorite brewpub, Dragonmead (I suppose its technically a microbrewery) is just south of Troy in Warren. Its on 11 mile rd on the S/W corner of groesbeck and I-696. They have great beer and great people. The owner really enjoys it and takes great care of the place. The staff know about beer, everything is always clean, everyone is friendly. I have never had a single beer that was "off" like you hear about in a lot of brew pubs. All in all it is a great place to spend an evening.
There are a lot of other places within a 15-20 minute drive. Just to name a few: Rochester Mills, Kuhnnen Brewing, Royal Oak Brewing, Copper Canyon and more. They're all great as well. I just don't go to them as often as I'm not as close to them as I am to Dragonmead.
Check out this site for a list of Mi brewpubs/microbreweries. http://www.beer100.com/brewpubs_l_to_n/michigan.htm