A bar without beer is no bar at all, and those who are serious about beer will want to tap their own keg, choose their own drafts and glory in every perfect pour.
Kegs for home use come in several sizes. Half kegs are the largest at 15.5 gallons (62 quarts), which comes out to about 200 12-ounce servings of beer (assuming about half an inch of head). Next is the quarter keg, which contains 7.75 gallons (31 quarts) and serves around 100 beers. The smallest units available are pony kegs and beer spheres, both of which are 5 gallons (20 quarts) each. If you're looking for something smaller than that, you might as well just be buying by the bottle.
When choosing a beer to keep on tap, consider the season. Keep dark beers like stouts or porters on tap for the winter, when their sweetness and heaviness make the cold a little more bearable. During the summer, it's best to lean toward a lighter brew like pilsner, wheat beer and India Pale Ale (IPA), which tends to mix better with bright days and citrus flavors.