@Phil, That one is nice, but it lacks kunkely goodness.
@Sto, Yea, I have to agree about the calipers not really working... Though, strictly-speaking, the icon is square, it's just that the side borders each have a bit that is transparent.
Here are some new things I was tinkering with:
Edit: see below.
The left one is square, but I have to have the question mark overlap to achieve it. The middle one it flat (not tilted) but still has a 3Dish iconiness about it.
Note that I put the pink wedge back on the left, because that's were the Windows drive properties puts it. The question mark definitely goes well with the "Joker" element. I'm surprised I didn't think of it! What color do you want it to be? For some reason I keep imagining it green... Also, look on your computer and see if there's a font you might like better.
Actually, 3D question mark floating above with drop shadow is okayish, I guess.. (right)