i 2nd DBAN.
However, NASA (well technically ontrac) was able to recover nearly all the data off of a hard drive from columbia. If someone REALLY wants to get recover the data, they will. Just pop out the drive and keep it somewhere secure if you're that paranoid.
Well it really depends on who you're trying to keep from looking at your data. If it's NASA and/or the CIA, then you're pretty well fucked unless you place a thermite charge above your harddrives... and so long as you don't mind burning down your house of course.
But for just about everyone else in the worls, DBAN and other similar products (all free I might add) will do the job wonderfully.
But again I don't see a reason to get rid of the HDD. Keep it around and use it as backup.