I would suggest Cal State Fullerton or San Marcos. Channel Islands and Monterey Bay are very nice but may be too isolated.
CSUF is within 10-15 min from Disneyland, sports venues such as Anaheim Stadium (Baseball) and the Pond (Ice Hockey/Concerts) and within 30 mins from the beaches. Downtown Fullerton has a nice restaurant and bar scene on the weekends.
CSUSM is near the San Diego area, so you have beaches, attractions such as Sea world and the Zoo, concert venues, restaurants and bars (in the Gas Lamp quarter) all within 30-40 minutes.