Fenders! They are the best of things, and they are the worst of things. My neighbor's recent purchase of a Priority Eight bicycle as a birthday gift for her son provided opportunity to explore fenders for more than just keeping water from my backside.
The young man commutes daily to school, and mornings are dark times now that we're back on regular time for the winter. Fenders can help, and I found a set in safety-yellow from Planet Bike that pair nicely with the kid's blazing-surface-of-the-sun Priority Light Set.
While shopping for the yellow fenders, I ran across some flat fenders from NYC Tour. They are essentially flat strips of aluminum curved to go around your wheels. I couldn't resist picking up a set, and I've carefully set aside my stock fenders while I give these new ones a go.
Fenders are mainly about protecting your backside, and I wouldn't want to commute without them. Fenders can also be about safety, and even personal style. They can be had in wood and bamboo as well the more common plastic and aluminum, and changing them up now and then is a fun way to express yourself and add some "spice" and variety to your riding.