Michigan DOT has some nice bike route regional maps you can order. (The paper ones are better than the on-line versions) Also, the Cherry Hill Bike Club publishes a nice map of NW Lower Peninsula. The combinatio9n is what I am using for my wanderings from Manitowoc to Luddington this summer.
http://www.cherrycapitalcyclingclub....odule_id=40089
http://www.michigan.gov/mdot/0,1607,...2734--,00.html