Jeremy,
The two major lakes in Madison, Mendota & Monona, are great for boating! They are good size and there's a small lock & dam with a channel connecting the two, so you can go back and forth between the two lakes. There's a couple of places to stop and eat on the water that are nice. I don't think there's any camping anywhere on the lakes though. They're surrounded by the city of Madison.
Unfortunately, with all the heavy rain, I heard those two lakes were closed due to high water. I think they may have opened them now, but there may be a no-wake rule imposed due to the high water yet.
Just an hour north of Madison is Green Lake. It's a beautiful lake and I think it's the deepest lake in Wis. I believe there is a campground on that lake and I know there are cottage/house rentals on the lake.
Another hour north of there is lake DuBay. It's a 6500 acre lake made up from the Wis River. Nice body of water with a couple of nice campgrounds.
Good Luck!
Crownline 180BR/4.3MPI
Allison SuperSport/Merc 280 Outboard