My two friends who were dating, decided on a Cosmo and Wanda Couple Costume from Fairly Odd Parents.
It was not only a very cute, fun idea, but also a very inexpensive one. All they did was buy pink and green spray on hair dye, and a package of wings with wands included. They took yellow construction paper and made stars for the wands and crowns for their heads.
Overall, it was a huge hit!