Check out La Jolla & the coves. Old Town. If you staying in the Gaslamp, you can walk to see The Midway & the Star of India. Go to Tivoli's, one of Americas oldest bars. Wyatt Earp used to drink there. If your'e going to Tijuana, park on this side of the border & walk across. Expect a bit of a wait to get back across to the US, especially on the weekends. The Zoo is great. Sea World if you're into that kind of place. The Birch Aquarium too. Cool museums in Balboa Park. Pacific Beach for day drinking & checking out really hot chicks. Some great restaurants in the Gaslamp, but make sure to hit one of the small independent taco shops & try a fried fish taco & make sure to try a California burrito
Is pacific beach an area in San Diego proper or on the outskirts of town?
Seems like a lot of good recommendations here, thinking of staying an extra day and pushing the flight if it works out.