D's is a classic pittsburgh joint. Their main fare is hot dogs with a wide variety of toppings, but their menu also includes other standard bar foods like Pizza, calzones, hoagies, etc.
But let's be honest, while the food is good, when D's comes up in conversation it is unlikely because you are raving about the "chicago dog" you had there last night: D's is widely recognize as the location of the "beer cave", a massive collection of beers from around the country and even around the world. Everything from little-known microbrews to fairly exotic imports like Delirium Tremens (the variety comes from the fact that they are owned by the same people as the nearby McBrooms beer distributor, I have been told).
A group of us grad students goes there every thursday night, so say hello if you're there. An added bonus is that the "new" side of the restaurant is already smoke free.