definitely go to north beach. good nightlife: great restaurants (mostly italian) right next to some awesome titty bars.
touristy stuff: fisherman's warf and pier 39; the ferry over to alcatraz; ghiradelli square, lombard street (crookedest street in the world) and check out chinatown (one of the largest populations of chinese outside mainland china) and japan town. haight-ashbury's cool too.
food-wise: get clam chowder in a breadbowl, some seafood, and take advantage of some mexican food (especially in the mission district, though it could get kinda sketchy certain places)
definitely check out pac bell park. great place; not a bad seat in the house.
if you feel like venturing over across the water, into the east bay, check out berkeley (telegraph ave.) and parkway speakeasy theater (best movie joint ever! they serve beer, wine and real food like nachos, pizzas, etc.)