The dells are nice. If you can get over the tourist trap part of it. We stay at Standrock campground. Located outside the dells. I like the Original Wisconsin Ducks tour and the Upper dells boat tours are also nice. If you are into mini golf and water parks then this is the place for you! If you don't like people then don't stay here! LOL
Door county is very nice. Lots of great places already mentioned there.
If you want something really interesting go on up to the Apostle Islands on Lake Superior, another really beautiful area.