My favorite Irish pub in dc is Nanny O'Brien's in Cleveland Park {red line}, though if you like something a little snobbier, go to 4 P's across the street. There are other options closer to the club, like Irish Times and The Dubliner which are by Union Station, or Fado {chain I think} and Irish Channel over by MCI.
Obviously, there are plenty of options, depending on where you are planning on staying, etc.