It's been a while since we've had a good discussion of downtown lunch options, and it would be nice if we compiled our notes into a single thread. So I'll start with some of my favorites (none of which will be a surprise to anyone):
Chacarero (Arch St./Province St.) -- Nuff said. My favorite downtown lunch.
Al's (State St.) -- It's kinda just a sub shop, but their homemade sub rolls make all the difference in the world.
Sultan's Kitchen (State St.) -- Great Turkish food.
Good Life (Kingston St.) -- For a casual sit-down lunch.
Sel de la Terre (State St., on the Aquarium side of Surface Rd.) -- When you need a place to bring a client.