While a lot of people enjoy the lightly sweet scent of bananas, aphids are repelled by it. You can use this to your advantage by placing banana peels around your plants.
Cut up banana peels into small pieces and bury them under a thin layer of soil around your plants — cover them well to avoid attracting backyard critters.
In addition to keeping the aphids out, the banana peels will also replenish nutrients in the soil, which will help out the plants drained by the insects.