Must-try restaurant in Philadelphia?

If I had to pick one restaurant to send an out-of-towner to, I would probably have to pick Mercato. It's an Italian BYOB that is in the Washington Square West neighborhood. Mercato has excellent food and is on the first floor of a corner unit that used to be a town home. It gives dinners an upscale neighborhood feel. BYOBs are big in Philadelphia, so I'd recommend that a tourist try a BYOB instead of a bigger restaurant like Le Bec Fin or Buddakan.