There are really 5 sand dune riding areas on the Oregon Coast.
I have highlighted each one, and listed the campgrounds that have dune access to those dunes.
If there are any questions feel free to email me back....
Horsefall
http://www.reserveamerica.com/camping/horsfall/r/campgroundDetails.do?contractCode=NRSO&parkId=70453
My #6 Not a bad place to ride, can be windy, but lots of dunes, popular, make rsvp early. No hook ups at the camp ground
http://koa.com/campgrounds/oregon-dunes/
My #7 Nice small campground, expensive, but full hook ups, a bit or a ride to get on the sand, not my choice of a place to stay
Spinreel (is connected to the Horsefall/Coos Bay dunes) http://www.co.coos.or.us/Departments/CoosCountyParks/RileyRanch.aspx
my #2 place on the coast, power & water hook ups, HUGE campsites, paved access roads, cheap rates, access to lots of dunes, close to coos bay / north bend, and you can ride on the beach
http://www.reserveamerica.com/camping/spinreel/r/campgroundDetails.do?contractCode=NRSO&parkId=73812
my #3 place on the coast, no hook ups, sites are small if you have a larger toyhauler or rv, easy access to the dunes and you can ride on the beach
http://www.myrtlewood-hauserrvpark.com/
My #5 haven't stayed here, large parking lot with decent sites, a bit of distance to the sand, no hook ups, can be REALLY busy on holiday weekends, close to coos bay / north bend,
http://www.co.coos.or.us/Departments/CoosCountyParks/RileyRanch.aspx
Riley Ranch OHV-Park
My #2 place on the coast, power & water hook ups, great campground, off-season rates, cabins too.
BIG sites for those with big haulers, and lots of toys.
Direct access to the sand.
Winchester Bay
http://www.co.douglas.or.us/parks/view_park.asp?id=57&features=&cnt=
my #1 place on the coast, no hook ups, large pull through sites, good camp host, close to Reedsport, easy access to the dunes, no beach riding, great dunes if you like big hill climbs and awesome views of the ocean
http://www.discoverypointresort.com/
My #4 not a bad place, pull through spots with full hook ups, some spots get small and it can get very busy and crowded, close to Reedsport, easy access to the dunes
Florence
http://www.reserveamerica.com/facilityDetails.do?contractCode=NRSO&parkId=70452
My #8 Not a favorite place of mine, no hook ups, basically just a large open parking lot with SMALL skinny sites, not a fan of the dunes, LOTS of wind, a bit out of town if you need supplies, dunes are usually very windy and can have lots of razorbacks from the wind, campground
http://www.sanddunesfrontier.com/
My #9 never been here
http://www.oregonstateparks.org/index.cfm?do=parkPage.dsp_parkPage&parkId=95
My #10 have stopped in here, decent sites, sand access, no hook ups, close to Florence
Sand Lake - never been there, never intend to go, very small, way over crowded, and too many accidents w/ injuries and deaths, too many people in a very small riding area - just my opinion.