I am not really a fan of those "one month of outfits, ten pieces of clothing" challenges. Why restrict one's abundance of garments? The utilitarian creativity of such frugal attempts may be exciting, but I'd rather mix it up a bit more.
Hence I am challenging myself to no repeats in any four week period: easy from the perspective of total clothing owned, difficult because I tend to get attached to a piece for no good reason and want to wear it repeatedly until it bores me (at which point I shove it in the back of the closet and - hey presto! - within a couple of months it's exciting again).
So far: this is day thirteen, and I'm still on track.