While you are in San Francisco, take in a play. We have our own mini theater district centered around the A.C.T. Theater and the Curran with other, smaller venues near by. While you are in the area, check out one of the restaurants on this list of where to eat before the theater from MenuPages.
Also check out the half-price ticket booth run by Tix Bay Area at Union Square for discount ducats to theaters in this area as well as around the city and Bay area. The service also has a large number of shows with discount tickets you can buy on line in advance. The Tix Bay Area site also gives a good overview of what is up with the theater and performance scene in the Bay area.