There are a lot of places to go. It just depends on your interests. If you want to goto the dunes then go to silver lake area. What are you specifically looking for?

Here are some web sites for you.

http://www.michigandnr.com/parksandtrails/parkmap.aspx
http://www.koa.com/where/mi/
http://www.michcampgrounds.com/arvcmich/index.php