The 9:30 Club isn't really a bar, it's music venue. You won't go there for the food or drinks or just to hang. You go there to see a touring band you like. And it's probably the best place in DC to see a band. Great accustics for a club holding maybe 300-500 people max. You can get up next to the stage and get hit by sweat from the band or go to the balconey and look down on the band. The one thing you can't do is sit down, so expect to stand all night. Try to buy tickets in advance at its website because it often sells out.
Pros: Great Music, Intimate Feel, Close to Metro
Cons: Food is marginal, Drink are average, Bad part of town