The Peninsula Trail and Grub Ridge trails both have marked campsites that are very far apart and totally private.  These are dispersed/primitive sites with a fire ring only.  Very remote feeling (except you CAN hear any loud cars/motorcycles at night from the main road over the lake). Light pollution is pretty low however, so good stargazing. 

Trails are in good shape and the Penninsuala trail is pretty easy. Grub Ridge trail gets moderate the further west you take it.  CAmpsites 10,11,12,13 are very accessible with a short hike and are fantastic spots.   

Lakeside spots are great also if you hike farther, but as others have said, drunk boaters tend to stop along the shore even though they are not supposed to. A few years ago boat access was limited to non-motoroized but not sure it is being enforced very well.  

All the same, the Deam Wilderness area is Indianas best for backpacking and backcountry camping. 

Down tower ridge road, to the east, just past the tower - turn right and the road there has lots of drive-in sites as well. These fill up fast on the weekends.