Preheat oven to 350. Lightly butter an 8x8 baking pan. Line bottom of pan with bread cubes. In a large bowl beat together eggs, milk, sugar, salt and vanilla. Pour the egg mixture over the bread. Dot with margarine and let stand for 10 minutes. Combine remaining sugar and cinnamon and sprinkle on top. Bake for 45 - 50 minutes, until the top is golden.