Don Pablo's Carnita's. I visited a couple weeks ago, it was a good as anything could possibly be. However, its not for the faint of heart, and I would not be real productive after a lunch there. I can't wait to go back!
Mundial Cocina Mestiza is my favorite Mexican restaurant in the city. It's just wonderful, with creative regional specialties. They're open for lunch during the week and brunch on weekends. You can see their menus on their website at www.mundialcocinamestiza.com