Coolest/most unique Nano accessories?

[AStar617]

Was strongly thinking of getting a 2gb Nano in Black, and wanted to know what you consider the coolest or most useful/unique Nano accessories. Links always appreciated.

TIA

 

[BRObedoza]

Nike+ sensor is a must if you run.

 

[cliftonite]

I got this case, though it hasnt shipped yet.