A few months ago I needed to wipe some hard drives at work before the machines got sold. For a couple of years I had been using the free version of Killdisk but it only does a single pass and isn’t open source so I though I’d look to see what was availible.
Auburn University has a great page detailing many of the DoD-Compliant Disk Sanitation Software programs currently availible. After evaluating several of them I’ve decided my favorite is DBAN which happens to be GNU Public Licensed which is even better. Since then I haven’t had any problems with the software at all and have found it to be both highly configuarable and easy to use.
PGP is good for wiping.