Pat O'Brien's is one of our favorite places to go to in the Quarter, especially in the summer. It's always dark, cool, and you can get a tasty, albeit a bit pricey, drink while listening to some tunes on the pianos.
This past summer I took some friends to New Orleans who had never been before, and the first night we did Bourbon Street & Pat O'Briens. The second night they only wanted to return to Pat O'Brien's.