We like Lower Pines in Yosemite Valley, Seacliff State Beach, and the PG&E campground at Lake Almanor.
Last week we stayed at Sam's Family Spa Hot Water Resort in Desert Hot Springs, CA, for three nights, and we will definitely be going back. It was so relaxing - very quiet at night, and hot water well-fed mineral baths up to 104 degrees. Very clean baths and pool area, although the rest of the campground was somewhat dated (but we like things that way). There is a huge game room with a ping-pong table and a billiards table. We haven't slept that much in a very long time. If I ever feel the need to run away to somewhere to relax (in the winter) I will definitely head out that way.
http://www.samsfamilyspa.com/index.html