I work downtown near the Market and find that I keep going back to the same places for lunch (i.e., 75% of the time I find myself inexorably drawn to La Vaca, the mission-style burrito window on First and Pike). I would love to break my rut and hear about other people's faves. Cost is an issue -- for example, I know Matt's in the Market has got an unbeatable lunch but I can't consistently drop $15 on lunch without breaking my budget. Any recs? I'm more interested in lunch to go but if there's a sit-down place worth trying I'll check it out too.