Ahhh.  Depends upon what you want, how far you want to go, and how $$.  Last time I was there I went to Herb & Wood in Little Italy.  Mediterranean.  C-Level out on Harbor Island is great for seafood.  Phil's BBQ in the Sports Arena area is good BBQ. Azuki Sushi near Balboa Park is really good.  Extraordinary Desserts is one of my favorite dessert places in the world. The Kebob Shop near downtown is pretty good Middle Eastern. 

Dislaimer, I have been back to last couple of years so things may or may not still be there.

You probably know tacos better than most of us, but Aaron Goodman had a nice post about SD tacquerias awhile back