(1169 Folsom) is doubly unique. First, it's SF's only beer-and-nothing-but-beer store: 350 bottles from around the world, all craft brews, no Bud, Miller, Coors, or other macrobrews. If you're looking for a hard-to-find beer, this is the first place to check.
Second, it's a small but great beer bar, with a rotating selection of six beers on tap and about half of the bottled beers in two refrigerators. Drafts are $4 & up, bottles consumed on premises are $1 over the retail price. Every Thursday night from 5pm until the beer runs out there's a theme flight of three or four 4-oz. tastes for $5-10; sign up for the weekly email newsletter to find out what they're pouring in advance.
The only problem with the place, from the prospective drinker's point of view, is that it's so small that it's often full. Best times to find a free stool are weekdays before 4:00 and Tuesday and Saturday evenings.