Combine eggs, milk, and oil in a medium bowl; mix well.
Sift together flour, baking powder, and salt; add to egg mixture, stirring well.
Spoon batter into a preheated, lightly oiled waffle iron, following manufacturer's directions. Cook 5 minutes or until brown and crisp. Remove waffle; keep warm. Repeat procedure with remaining batter. Serve hot with butter and syrup.
For cheese waffles, add 1/2 cup (2 ounces) shredded Cheddar cheese to batter before baking.
For ham waffles, sprinkle 1 tablespoon finely chopped cooked ham over batter of each waffle before closing waffle iron.