I like boldly colored headphones that have a different but complimentary color. One example are the v-moda bass freq in-ear headphones in "jaded green". As the name implies they favor bass over other frequencies but if you like the appropriate kind of music they're cheap but a good buy for at 29.95 on Amazon. (I've seen them go as low as $15, but they must be selling well because they've doubled in price in the last couple months. Still worth it IMO)
I also have my beats in-ear headphones that came with my former HTC One X, and I like the mix of their bold red color with the cyan of the Lumia 900.
In both cases they combine with the Lumia to make a very bright and colorful combo that I think is fun.