You can get a decent Department of Transportation state road map free by calling the state Department of Tourism hotline (800/432-8747). The best maps for snooping around the state are those contained in the Wisconsin Atlas and Gazetteer, available from any outdoors store or direct from the DeLorme Publishing Company (207/865-4171, www.delorme.com [1]). On a somewhat smaller scale than topo maps, the maps in this 100-page, large-format book are absolutely indispensable for exploring the back roads.
Topographic, planimetric, and 7.5-minute quadrangle maps can be obtained from the Wisconsin Geological and Natural History Survey (3817 Mineral Point Rd., Madison, WI 53705, 608/263-7389). The 7.5- or 15-minute maps cost $3.50 each. County topographical maps (1:1,000,000 scale) are available for $4 each.
Links:
[1] http://www.delorme.com