Create your own defragger!
Only for the experienced coder...I could probably do it, but i wouldn't trust myself to debug on my machine :).
The challenge is to write a defragger that runs faster than the "standard" windows degragger. It can be either a dialog or console app, but it must have some sort of GUI (including progress meter, and perhaps those nice little rectangles that show how data is being moved). Just a thought.