I've tried Ubuntu (back on Jaunty at the minute - touch wood), Linux Mint and Fedora 10 this week. Just discovered VirtualBox so I think I'll be trying a few more. First impressions of Fedora 10 are very good - potential candidate should Ubuntu decide to act up again.
That Linux test suggested Ubuntu, Mandriva, Fedora 10 and OpenSUSE so I seem to be on the right lines.
I've also tried Open Solaris which is nice but sort of backing oneself in the corner in terms of compatibility and support.