Any fruit, especially berries. Raspberries and blackberries, too, if you have them. Frozen is fine. A *little* syrup can go a long way. You could make a simple-ish apple and cinnamon sauce (shop apples, add a little water, simmer and reduce) and throw in some walnuts.
Also, if the waffles are being made to order: add fruit to the waffle batter and serve the waffles 'naked'. And there are also 'savory' waffles rather than sweet ... serve with cheese and the like (though there's still calories there).