Grease a 13x9x2 inch baking dish, arrange sliced bread in dish overlapping if necessary. In bowl, combine eggs. milk, spinach, salt and pepper. Pour over bread. Sprinkle with cheeses. Cover and refrigerate for 8 hours or overnight.
Remove from refrigerator 30 minutes before baking. Bake uncovered @ 350 for 40-45 minutes or until lightly browned. Serve warm.