Ice Age Trail-it's heavily regulated, but can be some gnarly scenic hiking (I guarantee you you'll see at least a hundred deer and as many wild turkey in a 15 mile dayhike) and I believe they have a cabin system set up for some sections of the trail. I'm very familiar with the Greenbush trail system, which it cuts through-another great spot for dayhikes (great by WI standards anyway) though at this point I'm sure the mountain bikers and cross country skiers have that place moving so fast you would have to be constantly watching your back so some 200 lb 50 year old guy doesn't wind up plowing you in the back doing 30mph on his fat tire beast (like my Dad-he's a big trail bum there). The kettle moraine in general is good for midwest standards, just for dayhikes though... Parnell Tower, Long Lake, Butler Lake... I grew up about 20 miles away from the most of it so Dad and I spent most of our weekends biking out there on road bikes and hiking or on mountain bikes and cruising the trails. I have good friends still back in WI that are big into backpacking and try to make the most of what few overnight trails there are-they have some sort of facebook or yahoo group or something and do longer trips at least once a month. I know Pictured Rocks is their hot spot.
I can't believe I forgot Devils Lake. One of the few places in WI you'll have measureable elevation change, though it will still be less than a thousand feet... an extremely deep glacial lake surrounded by 400 foot cliffs on all sides. It's a hot spot for family camping, camp on one end of the lake, hike the 20 miles around it one day and spend the next day on the lake fishing, swimming or canoeing. No matter what you're pretty much trying to supplement for the real thing. I know big blades are illegal, most people look down on using any kind of wood found on the trail for a fire (my buddies have to take stoves) but it's most certainly better than nothing.