We have camped at both Beverly Beach, and South Beach. I actually prefer Beverly Beach because of the nice wooded areas and the walk to the beach isn't very far... however, I have only camped at both in off seasons. If you haven't been to either one... they are both nice. Be sure and "take in" the lighthouses along the way if you are driving along the coast! Here are a couple of photos from both South Beach and Beverly Beach.
Oh such difficult decisions!
Have fun! Enjoy the Oregon Coast! Mid September should be nice, but you could have rain... (actually we'd love to see some!)