[Descant]

Gunstock isn't directly on the lake, but has tons of things to do with reasonable prices. If you're not boating every day and will drive to do things, e.g. climb Mt. Major, go to Funspot, then it is a choice worth considering. Lodge for rainy days.
Probably full up for 2014, but the Appalachian Mountain Club owns Three Mile Island with family camping (rustic cabins, communal dining). All inclusive for quarters and food, and discounts for AMC members. If you've never been to summer camp on a lake as a kid, consider this. You have to make plans and apply early, (Jan-Feb?) and it probably helps if you can be a little flexible on your week. Runs from Sat.-Sat. I think.