I purchased a server about 6 months ago and it's been a huge learning experience. I'm now going to sell it - I've sold the sites that I was hosting on it. I'd like to sell it with formatted hard drives... what's the best way to do that? Is there anything else I need to do to it? I'm not storing any crazy personal information or anything on it.
It was running Ubuntu Server
What you might not think is crazy personal information still might be useful for somebody else. I'd recommend downloading a copy of DBAN and running it over the drives on the server to make sure everything is really gone.
Hunt around for 'Ultimate Boot CD'. You can burn an ISO of theirs to A CD, boot from it and select form one a a few tools that will do a multi-pass wipe of the drives.
Otherwise, blow the dust out of it and perhaps install a fresh copy of the OS, so it's more attractive as a purchase. It helps to demonstrate that it boots. :)
Unless you are selling the server as a black-box-providing-service, I would suggest that most people who get the server will be formatting the disks and installing their own OS as the first thing that they do.
I also endorse the DBAN as the way to go.
Badblocks in write mode would be my choice. Available on every live cd/usb distro.