As I have told many inquirers on this board, Tokyo has more restaurants per square mile than any place I've ever been. It depends on which side of the imperial Palace you're staying on (those are BIG grounds), but some neighborhoods have more restaurants than others. For certain, any department store will have a restaurant floor or two where you can choose from a wide variety of inexpensive to mid-priced restaurants.

Restaurants in Japan tend to specialize in one or two types of food, so what I do is wander around and find a place whose window display looks appealing.