I'm going to San Diego in either August or September. Do you know of any good camping spots between there and Disneyland? (I'm not opposed to driving a bit out of my way either.)
San Clemente State Park and San Onofre State Park are great spots close to the water and are roughly an hour north of downtown san diego and about 40 min from dland
Depending on the type (and intensity) of camping, there are a lot of different spots. I agree with Reuben with San Onofre State Park, I've heard that one is pretty nice to hang out, be by the beach, etc. I think it's formally called San Mateo Campgrounds (I think, that's basing on memories of signs as I drive by). If you want to be in San Diego, one of my absolute favourite areas is Encinitas/Carlsbad and there are two beaches that allow tent camping: San Elijo State Beach and South Carlsbad State Beach (scroll down in the link to get to the descriptions). I don't know anyone that has actually camped there so I don't really know facilities/offers/what it's like, but...I just love those beach towns so I figured I should suggest it :)
If you don't mind desert, Anza Borrego Springs and Ocotillo Wells are supposedly some good places. The entire Ramona/Julian or Santee Lakes areas are a pretty big camping destination, or at least the ones my friends tend to go to (we live North Inland San Diego).
For places that are kind of between beach and the super dry desert, I've heard of Palomar Mountain, my brother's been up there and he really likes it for the views and stargazing things--but I'm not sure how reliable that would be, during fire season it gets pretty dry and I think they may close off parts of it for safety reasons so you'd definitely have to research it a bit. I've driven by Lake Elsinore and heard it's pretty nice, too.
Sorry for the long reply! I don't personally camp so I can't give details about it, but those are the ones friends have talked about and always want to go to.