+1 on Lost Maples nice place.
Pecan Park Retreat just east of San Marcos. It is a private campground on the San Marcos River. Most weekends it is nowhere near full, but this time of year it can be full. Nice restrooms, owned by really nice folks. They cater mostly to Boyscouts/Girlscouts and church groups. There is no alcohol allowed, but be discreet and you are OK. Tell em Rodney Swann sent ya. Great riding starts west of town. If you camp there let me know, I live about two miles away and will come visit y'all.
Garner State Park, great place, very crowded in Spring and Summer. Best to visit during winter. Right in the middle of the best riding in Texas.
Krause Springs near Dripping Springs, 32 springs, beautiful place and near good riding.
Inks Lake is beautiful and near some great riding.
Stay away from Lockhart. I am not aware of any campgrounds other than the State Park and it exists to support a golf course. There are only a handfull of campsites and they are not very pretty.
Guadalupe State Park on the Guadalupe River, very beautiful and near good riding.
Kerrville-Schreiner is a nice place, on the Guadalupe river, and near great riding.
I have been wanting to go check out Camp Wood in Leakey, it caters to motorcyclists and is in the middle of the best riding in Texas.