Anza-Borrego Desert State Park
Full of information on the Anza-Borrego Desert and getting the best out of it.
http://www.anzaborrego.statepark.org/park.html

California State Parks – Anza-Borrego Desert
For information on Park fees and reservations.
http://cal-parks.ca.gov/default.asp?page_id=638

Cleveland National Forest
All information on current weather conditions, camping reservations, fire risks, and generally getting the best out of the Forest.
Sorry, the site is currently down!

Cuyamaca Rancho State Park
All your hiking, bike trails, camping and reservation information to help you enjoy 25,000 acres of wilderness. Don’t forget the Stonewall Mine site, and from the top of Stonewall Peak, you can see the Salton Sea to the east, and just about to the Pacific to the west.
http://www.cuyamaca.statepark.org/

Los Penasquitos Canyon Reserve
Los Penasquitos (meaning little cliffs) Canyon Preserve lies between Rancho Penasquitos and Sorrento Hills to the north and Mira Mesa to the south. The San Diego Sea to Sea Trail runs through the eastern half  of the Preserve.
http://www.sandiego.gov/park-and-recreation/parks/penasq.shtml 

San Diego County Park & Recreation
Your guide to the 78 facilities managed by the Department, covering more than 35,600 acres, open year round.  And soon you’ll even be able to make your camping reservations on-line.
http://www.co.san-diego.ca.us/parks/

Torrey Pines State Reserve
The Trail ends, or starts, at the beach here. 2000 acres of land as they were before San Diego was developed and one of the wildest stretches of land on the Southern California coast. Includes the chaparral plant community, the rare and elegant Torrey Pine trees, miles of unspoiled beaches and a lagoon that is vital to migrating seabirds.
http://www.torreypine.org/