A couple of ideas for you...
The Mexican Restaurants in Old Town are pretty good. May be a tourist trap but the food is authentic. Large place at the N end where they make homemade tortilla's is my favorite, also heard good about El Agave.
Not too far away in Hillcrest is Phil's BBQ. Only made one visit but I'll go back.
SOme decent steak options...Rainwater's on Kettner and DOnovan's Chop House are both excellent.
At the S end of the Gaslamp Quarter, right next to the trolley stop is an interesting place called Tin Fish. Huge portions, good (generally fried) seafood items and great clam chowder.
If you want to go touristy you can go to the Kansas City BBQ right at the Seaport Village trolley stop. Restaurant/bar where bar scenes from "Top Gun" was filmed. Adequate food.
If you really want to do it up, go down about an hour south into Mexico to Puerto Nuevo and experience lobster at its finest (and reltively reasonable). I'll link some info. If you go, please drive safely, stay on the main roads and get Mexican insurance.
http://www.bajalife.com/bordercrossing/dininglobster.html
Bob in RSM, CA...yes, I know, it's a long way from Chicago