In Del Mar, there is a place called Jakes. I am a big fan.
In La Jolla, if you want to experience a first class meal at a great rate go to the George's at the cove for lunch and sit upstairs on the patio. Greatly reduced prices for great food.
I hate the GasLamp district. Its like 70%West End in Dallas and 30% Sixth Street. As someone who commuted to San Diego for two years, the locals agreed it was a tourist trap.
If you want something a little off the beaten path, try going to the Rancho Vallencia Resort. A good drive, but a nice drive. Tons of orange groves and lemon groves, etc. Nicely manicured spot. Not exactly cheap, but again for a weekend lunch I recall it not being outlandish.
For a local cheap eat, try World Famous in Pacific Beach. They have some super cheap taco special. I forget when and how it works. But a good spot.
For beaches, I recommend Torrey Pines State Beach. Very nice spot.
I could come up with more, but that could get you started.
[This message has been edited by Objective Aggie (edited 4/29/2009 10:59p).]