Cut tomatoes into 1/4-inch-thick slices. Arrange half of slices in a large shallow serving dish; sprinkle with half each of sugar, salt, and pepper. Top with remaining tomato slices; sprinkle with remaining sugar, salt, and pepper. Drizzle vinegar evenly over tomatoes. Cover and chill 1 hour. Turn tomato slices, coating with vinegar mixture, before serving.
*Red or yellow tomatoes may be substituted for green ones, or use a mixture of all three varieties.