I haven't seen it, but what I thought somebody should devise is a drive bay
charger/dock for PDAs, MP3 players, etc. (maybe compact cameras)
i.e. one provide socket to insert the device(s) where they could be stored (out of dust), charged, and be connected to the computer.
Each device might have its own fitted socket that it would slide into and mate with a connector. More generic would be a drawer with charging/connection cables in it (but that would be a bit of a bother finding the right cable and hooking it up).
How about that Zalman power use meter that was recently reviewed here.
Wire up a microcontroller, some LEDs and make a blinkinglights panel http://en.wikipedia.org/wiki/Blinkenlights
(Use multi-colored LEDs for that festive holiday look).
Put in an LED text display panel (set up as a ticker for SPCR forum posts
Add a larger or second LCD or OLED panel (http://www.lcdgallery.net/
) - you can never have too much bling.
A clock (of whatever persuasion you want - hack a day has all sorts of clock display ideas).
Would be okay place to mount a fingerprint reader or a magnetic stripe card reader.
Come to think of it, if you have some open space inside the computer around it you might even be able to shoehorn a label printer in there.