Can't believe no one has mentioned my very favorite restaurant in the city: Taverna dei Mercanti, in Piazza dei Mercanti in Trastevere. Probably the best grilled meats I've ever had--the salsiccia is particularly wonderful. Just get the griglia mista; you can't go wrong with a selection that usually includes the salsiccia, some kind of beef, pork, and/or lamb, and quail or squab, depending on what they have fresh that night. Plus, the atmosphere is unbeatable; it feels very medieval, with torches illuminating the outdoor seating area and wooden beams criscrossing the dining rooms. They have great pizza as well (though Remo in Testaccio is my choice for best pizza in Rome), and best of all, there is no pasta on the menu. It's a great break for when you get tired (yeah, right) of carbonara, all'amatriciana, arrabiatta, etc. Plus, it's close to a number of great bars, including my personal favorite, Molly Malone's--though that place has gone downhill a bit since Andrea sold it in 2003. Still a good spot for a Guinness, though.