When in SF, go to Bi-Rite. Perhaps hesitate to go with one scoop of strawberry on top and one scoop of cinnamon/snickerdoodle cookie ice cream on a cone... but don't hesitate long, because the long line of people behind you won't love it. And when you receive the most perfect aforementioned combination of ice cream flavors that you've ever tasted, thank me. And I will be thanking the guy behind the counter who recommended it to me.
Bi-Rite: 3692 18th St or 550 Divisadero St.
I may need to sample all the hip ice cream shops in the city now that I've had this one.