So it may be an international franchise now, but the first Porterhouse was opened in Dublin (in Temple Bar) in 1996, and was Ireland's first brew pub.
The Porterhouse Central is opposite Trinity College on Nassau Street, and is a long and crowded room with a long and crowded wooden bar. There are scores of local and international beers available, including the handful brewed by Porterhouse, and if you can't decide what to try, get the three-flight taster for just a few euros. (Hint: Try the Oyster Stout.)
The beers are all reasonably priced, and the pub has a good atmosphere with a mixed clientele of locals and tourists. There's a decent selection of pub grub available too—the wings look particularly good.