Hey, I'm a San Diego native too!!
We rock!
At any rate, my fellow San Diegans, and the SD fans, are all spot on with their suggestions. Again, I will reiterate that the Gaslamp quarter is a good place to go for nice historical sights and shopping by day and a hopping club scene at night. Another place worth mentioning is Pacific Beach. PB is a beach community with some interesting shops and a solid nightlife as well. Other good suggestions are: Balboa Park, the San Diego Zoo (which is next to/in Balboa Park), Horton Plaza, La Jolla, and Old Town. Pretty much the same stuff everyone else mentioned.
For food, you might want to visit the famous Corvette Diner in Hillcrest (which is also very interesting). Make sure to ask your waitress for lots of things like napkins and straws.
http://www.cohnrestaurants.com/cohn/...tte/index.html
Also, you *have* to get some Mexican food and may I suggest an establishment owned by my friend? El Indio restaurant is located near to downtown on India Street at Washington St. You can get a good Mexican meal in Old Town as well, but the locals in the know go to El Indio. Just be careful, the lines get really long at lunchtime.
http://www.el-indio.com/
Speaking of Mexican food, you can catch a trolley out of downtown San Diego to San Ysidro and then walk across the border into Tijuana.
Have fun!
.....Kelly