We have made an annual trip out to the Hills for going on 10+ years now. I think this year we are up to 9 family's. Let me know what your looking for and I can give you some ideas on where to go. It's a blast out there with endless riding potential.
I've ridden the Centennial trail (Nemo area) but that was quite a few years ago. With the kids I just can't find the time to get out there again (that will change as they get older). Some friends rode up in the Deadwood area as well, the pictures looked like a good time as well. A few old mines to explore and other stuff. It was a good time and many miles of trails (maps are online).
Camping on public beaches is not allowed,There are also some nice camping area like Black Hills National Forest for camping. I planned annual trip for this Hills with my friends. this area is also good nice for camping and riding.