Mittens are definitely my favorite thing to knit. There are just so many beautiful patterns out there. They are also small, but can still challenging projects. I am absolutely in love with Latvian mittens personally.
So, one tip that I have for jazzing up a pair of traditional looking mittens and turning them into a hipper looking accessory is to use non-traditional colors on a traditional color pattern. I think this creates a very playful effect (i.e. purple and green norwegian mitts!).