[Paleo Conservative]

big magnet?

That's what the bulk eraser is. I'm just unsure of how effective it is.

[JerseyHighlander]

If you can get the drive to spin up at boot, you can try Darik’s Boot and Nuke (DBAN), Shareware.
If you aren’t concerned about the DoD trying to reconstruct your hard drive, disassembling the drive, and taking a electric drill and pressing across to shave, and through to puncture, is a sure bet.

[Red Steel]

Here:

http://www.semshred.com/contentmgr/showdetails.php/id/606

[patton]

I suggest Gaussian elimination.