It ain't fancy, there's no place to sit and it isn't really close to anything, but it's some of the best ice cream you'll ever eat. Our whole family loves ice cream, and we make a point of tracking down the best ice cream in any city. Mitchell's is by far the best ice cream in SF. It's been around forever and always has a line (be prepared to wait). We went regularly when we lived in SF and now stop by anytime we visit. The ice cream is rich and flavorful, and they have some really unique flavors. Be sure to try before you buy.
A hint to newbies: They use a number system, so step inside and grab a number as soon as you arrive.