Beyerdynamic Custom One Pro ($199)
Cosmetic customization of headphones has been around for a while now, but I believe this is the first time I've seen a headphone with customer adjustable bass response. The photo to the right shows the side of the box with a graph for the Custom One Pro showing the bass response in the various switch settings.

I measured the headphone's frequency response in the four different positions (see below), and while it doesn't quite look like what's on the box, it certainly did change the profile of the bass section of the frequency response, and frankly I was pretty impressed with the feature. I reckon we'll see more of this type of thing as time goes on.

The headphones also have replaceable headbands and cables of different colors, and a panel in the earpiece can be customized with an image from a .jpg of your choice for around $20.

More information on these cans can be found on Beyer's website product page; in this Head-Fi.org thread; and at this Headfonia review.