KLAIT said:
If inexpensive is important, I would lean away from the Dells. It is a very expensive place.
Yeah, I have to say that it is. I LOVE the dells, and it's always been a good option for us, as it's main focus is water and swimming, which works well with the age spans we have of almost 12, almost 10 (boys) and 4 yo girl. We have a tough time finding stuff they all like or places where we don't have to "divide and conquer" so that each group of kids gets to do what they want. Even at the Dells, there's a bit of that, but they all LOVE the wave pool. My fav. place to stay is the Wilderness Lodge, it has tons of both indoor and outdoor slides/rides and the outdoor stuff is heated! (Not a lot, but heated none-the-less!) . IF you'd be willing to sit through a presentation for Fairfield, you can get a two day free stay. It works even better, from what I hear, if you can get a Fairfield owner to "recommend" you, they get some sort of bonus points and you're more likely to get the room free. (And, if they're in a generous mood, your friend may get in free, too!)
http://www.wildernessresort.com/ for the regular web address to check it out.
You can get slightly better deals if you're able to travel with another family and can rent one of the condos or townhouses. Also, the last week of August is the cheapest summer week to go. The Wisc. kids are back in school, so it's "off season" for them. It goes up again Labor Day weekend, but otherwise, it's cheapest.
They have a ton of non-water things to do, too. They have the Wisconsin Dells Ducks, a bunch of go cart places, Tommy Bartlett's ski show, a robot world, Ripleys, etc etc etc. Lots and lots to do, but as others have said, pretty expensive in the summer. Here's a link to the conv. and visitors bureau
http://www.wisdells.com/home.cfm?flash=1
Have you checked out Cedar Point? I've never been, but from what I understand, you can stay nearby and have beach time and then go to the park, which has been rated the worlds best roller coaster park.