Love Michigan. Saugatuck and Douglas Area (even Holland Michigan and someone suggested South Haven - all nice) has great beaches, wonderful eateries, ice cream and fudge shops, lots of shopping and other local activities. Oval Beach (great walking trail w/ dunes) and other lovely beaches, Crane Orchard, blueberry picking, horseback riding, nice trails in the woods. accommodations run the gamut - B &B's, hotels, camping, home/vacation rentals. Week-ends are very busy!
St. Joseph Michigan is lovely too. Much closer. Love the Pier w/ the lighthouse - awesome walk (Michigan is known for their lighthouses) Great beach, nice park on beach, cute shopping, nice eateries. This can also make a great overnight trip as it is so close.
Also, Galena IL is a very cool place to go and Mississippi Palisades State Park is just beautiful! And... it's been a while but Door County WI offers a lot to do. Lovely trip. Peninsula State Park is wonderful with many camping options, as well as all the other accommodations that Door County has to offer.
Best thing about Michigan are the sunsets on Lake Michigan!