What programs do you recommend to clean a drive to prevent recovery?

I've got a spare drive that i'm passing on to a work colleague, the problem is that the drive used to contain all my private data and was in use until very recently.
Obviously I have moved the data off the drive, now I'd like to use a disk cleaner to obfuscate the platters to try and prevent him from running one of the free disk recovery programs on the drive.

What free software would you recommend?

(P.s, I also couldn't find anything about this in the FAQ, so if we get some good answers can the mods please consider adding this QA in?)

Cheers all!

http://cmrr.ucsd.edu/people/Hughes/SecureErase.shtml
Or any program that gives you the option for a single pass of zero's or anything. If you use Linux or have a livecd dd if=/dev/zero of=/dev/DRIVE bs=1M .
Ignore anyone that says to do multiple passes and all that nonsense. It's impossible to recover data after you've written over it.

Excellent, thanks.

PEDO!

Yes, you are correct, I do have a foot fetish.