Rockbox - Alternative iPod Firmware
An upcoming alternative firmware for the iPod called Rockbox allows users to replace their iPod's firmware (operating system) with a custom one. Rockbox offers many advanced features for audiophiles... including much more adjustments and customization. Since the code is open, users are encouraged to create their own themes as the one pictured here.
It's still in development, and you do have to give up some of niceties that Apple offers - such as iTunes syncing and Protected AAC (iTunes Music Store) song playback. But, hey, you get OGG support...