Most people save tomatoes by putting them in some plastic-wrap in the fridge or something like that, but chowhounds in the know say that fridges kill raw tomatoes. Try this instead: put some oil in a covered container. Sprinkle the cut end of the tomato with a little fine salt, then place the cut end down into the oil and put the lid on. This will keep the tomato fresh for a couple of days at room temperature (Karl S).
Board Links: Saving tomatoes.