Not that there are many. I found only seven true Irish beers widely available: the real king of beers, Guinness (in two forms), Caffrey's Irish Ale, Harp, Wexford Cream Ale, and Murphy's Irish Red and Stout.
Harp hails from Dundalk, Ireland (although the version available here is brewed in Canada) and suits those hankering for a lighter, lager-style beer. Lagers -- like Coors or Budweiser -- are the most popular American style. However, Harp is far superior to its mass-produced, watered-down cousins, and perfect for those who aren't yet initiated into the heavier, chewier Irish stouts. Harp is clean and crisp and features a pleasant bitter aftertaste.
Another lighter beer is Murphy's Irish Red, which recently underwent a marketing makeover from Murphy's Irish Amber. Commonly found in tap form, but also available in kegs and bottles, Murphy's Irish Red is a slightly bitter, crisp, red-hued ale. Harp is the better choice if you're looking for a lighter experience.
FYI: Although the marketing will fool you, the reddish lager Killian's is absolutely not an Irish beer. Irish Killian's ceased production in 1956, and Coors Brewing Company licensed the name to produce it here at home.
Truly the best-known Irish beer, Guinness Stout has a dogmatic loyal following. Aficionados are almost as persnickety as diehard wine snobs, seeking the perfect temperature (42 degrees to 46 degrees) and the perfect amount of head (1/4 inch to 1/2 inch from top of pint). If they're trapped without a pub, they'll deign to quaff the canned Pub Draught version released a few years ago. It comes complete with a nifty nitrogen capsule that releases thousands of tiny bubbles upon opening to promote proper froth. It works. The regular bottled Guinness, labeled "Extra Stout," tastes flatter and has less oomph. Loyalists insist on drinking all Guinness from a pint glass.
Murphy's Irish Stout is a lighter stout version that is slightly milder in flavor and less bitter than Guinness, so it's a good introduction to this variety. In addition, its silky, creamy froth sliding down the sides of the glass provides good drunken entertainment.
Wexford Irish Cream Ale also sports the fun nitrogen gizmo, but I gotta say, this beer didn't win any tasting contests -- not even among heavy beer fans. Cream ale is supposed to be a blend of lager and ale, light in body and pale, but Wexford didn't come off that way.
Caffrey's Irish Ale wins the popularity contests, no longer available except in small quantities left over on shelves. Complete with the nitrogen capsule that mimics the pub experience, it's lighter in alcohol (4.2 percent), sports a dark caramel-colored creamy foam and tastes faintly of salty, hoppy bitterness. The rumor is that Coors bought Caffrey's, and cut off imports since it was hurting Killian's sales (Coors has not confirmed or denied the rumor), but this is an excellent St. Paddy's Day choice if you can find it.
So like supporting your independent restaurants rather than chains, it's definitely PC to reach for an Irish brew on St. Paddy's Day. Skip the Bud or Killian's, and reach for the real thing.