You shouldn't have to radically redefine what a cake can be to make it stand out. "Fruit" and "wedding cake" may not sound like the most obvious pair, but, as many dissimilar couples can attest, opposites do indeed attract. In this pairing, fruit's sweet, natural flavor can add a surprising and welcome complement to a sugary set of cake and icing.
Now, there's a couple of ways you can go here. You can have a traditional, tiered cake with various sliced fruits placed on top of each section, filling up all the empty space between tiers. This is a great way to show off both a classic and contemporary look at the same time, and it can help your wedding's most important dish conform to your ceremony's theme or location. If you're having beachside nuptials, go tropical by topping your cake with pineapple, coconut and tamarillo. Strawberries, blueberries or currants, on the other hand, would be perfect cake toppers for a garden party theme.
If you'd rather give your guests a fruit-filled surprise, you can always stuff fruit inside the cake. The fruit you use should depend on the flavor of your cake and icing, but unless you're trying to cram fresh watermelon inside a mocha-flavored cake, you should be fine. Berries and citrus go with just about anything, but don't be afraid to bring a few pieces of fruit to your cake tasting if you can't decide.