There are usually 7 or 8 beers on tap at 21-A, and also a few bottled guest beer selections.  The styles range from a light cream ale to stout and barley wine.  Beers are all very clean and typically pretty dry, leaving nice hop aromas.

Most of the beers are named after retired San Francisco breweries or for San Francisco neighborhoods.

Here are some beer offered:

Amendment Pale - Good California style pale ale.  Moderate bitterness is well balanced with a nice body.

North star Red - One of the best red's available in San Francisco.  It has a great balance between the malt and hop character.  Not at all fruity or estery like many reds/ambers can be.

U.S. IPA - One of the great IPA's this city has to offer.  Tomahawk hops add to the distinctive aroma.  Very bitter, but not at all overwhelming like a lot of IPA's can be.  It has a great flavor that can be enjoyed all day. (for beeraholics like me at least)

Shot Tower Stout - A foreign style stout that rotates between being served on nitrogen and on CO2 (currently on CO2).  It is a wonderful example of a foreign stout, with some very nice sweetness.  It reminds me a lot of the Old Scout Stout from 20 Tank.

Watermelon Wheat - Fermented with 500 pounds of seedless watermelon.  A very drinkable, light and refreshing beer that is surprisingly dry.

Mission Bay Maibock - A very good example of a blonde German style bock beer.  It has a good wetness factor and is very easy to drink.  It has some good bitterness from a generous dose of Hallertauers.  

South Park Blonde - Very light, refreshing, and effervescent.  A cream ale by style.  Low bitterness with a mild Saaz aroma.

Second Street Cut Pilsener - This is a very nice pils.  I gave it my toughest tests and it passed all of them.  It has a very nice bitterness to it, and it has a nice Saaz aroma too.

Oyster Point Stout - Brewed with actual oyster shells in the boil to give it a slightly salty taste.  It's not very noticeable, but it does add to the flavor.  It's an awesome stout once you get past the oyster shells.  Check out some pictures from the oyster eating part of the brew.

O'Sullivan's Irish Ale - A red ale served on the nitrogen faucet.  It has a lot of dark caramel malts that lend highly to the slightly burnt malty taste.  The nitrogen provides for a very smooth drinkable taste.

Wheat - American style wheat.  Very dry and not overly cloudy.  Also refreshing.  Served with lemon, so if you don't want one, make sure you ask when you order.

Pippo's Porter - Very clean, smooth, kind of light tasting porter.  Not very robust like some porters can be.  This one is on the lighter side.  Nice color and mouth feel.  It gets most of its taste from chocolate malt.

Old Cornelius Barley Wine - The hoppiest barley wine ever.  Several dry hop additions give this one a huge hop nose.  Aged for over six months, this barley wine is very smooth.