Are there any good campgrounds between San Francisco and Santa Cruz ?
South of Santa Cruz
The best ones are South of Santa Cruz. See state parks link above. There is an RV Campground in Half Moon Bay right by the Harbor. Ashphalt surface. That would not be on the State Parks list.
One other note
Just FYI. Be aware that Manressa is nice, but you have to park and carry your stuff down to you campsite. I like New Brighton best and Sunset 2nd best.
BETWEEN SF and SC
The suggestions are good. New Brighton is gorgeous, but it’s always completely booked well ahead of time during warmer months. If you’re looking for camping spots between SF and SC, there are limited options.
A short distance inland is Butano State Park. Great sites in a quiet park filled with redwoods. Another option, right on Hwy 1, is the Pigeon Point Lighthouse hostel. That gives you a bed indoors in a beautiful setting. It’s cheap, and there’s a hot tub. Once you get to Santa Cruz, there are a few more options in the mountains around town, but between cities, I’ve just given you the list.
Another option is stealth camping. There are lots of places that look inviting to camping, and at which people do occasionally camp, but camping is not specifically permitted and may, in fact, be forbidden. The best practice is to arrive late, leave early and take steps not to announce your presence. Not advocating this approach, but it works for some people. 
Thanks Everybody.
Not Much To Add
We do all our camping south of Santa Cruz,so I don’t have much to add.
We generally like New Brighton, which is just south of Santa Cruz, but it is very difficult to get spots there. I also like Sunset Beach, but that is 15 miles south of SC.
Our back up spot is Big Basin. About ten miles inland from SC, but easier to get spots.
A couple notes, SeaCliff Beach is for self contained RVs only. Manressa is a walk in site. Half Moon Bay is very open. Kind of like camping in the parking lot. I would only do it a a last resort.
Camping Near Santa Cruz, CA
Henry Cowell St. Pk. located in the Santa Cruz Mountains near the town of Felton is another option. Only about nine miles plus or minus from Santa Cruz proper.
Barracuda, everytime we drive down
south of S.C. seems there is always plenty of open spots… is it always like this ???