For a funky restaurant (before the beer) in North Beach, you can try the "Stinking Rose" where food is added as seasoning to the garlic. It's a bit touristy (because it has been so successful), but definitely an experience to remember and the food tastes good. Beware of the garlic ice cream though :). If you like sushi, the best sushi I've had outside of Japan is at Ebisu at 9th Avenue between Irving & Lincoln (Right off Golden Gate Park). They don't take reservations, so be prepared to wait in line to get in - its definitely worth it.
Another less expensive but extremely authentic restaurant is the Canton Seafood & Dim Sum Restaurant in the heart of SOMA (1 block from my office at 655 Folsom). If you know Dim Sum (where food is carted around and you choose what you like when you see it) theirs is hard to beat. As good as in Hong Kong. This also locates you in the heart of the technology center in SF, and you can check out all the highrises springing up on this side of Market.
To really dial in the perfect place given the genre of food and price and location and atmosphere that you want, go for http://www.zagat.com/ . (I think we have more restaurants here per capita than anywhere else in the US)
What mode of transport will you have during the day? (To give you some ideas on what to do)