If you've ever asked yourself which distro is right for me? then you might be interested in trying them all. :D
But I have some further suggestions:
- {Free,Open,Net,PC-}BSD
- Solaris, OpenSolaris, Nexenta
- ReactOS
- Plan9
- Minix
- SkyOS
- GNU Hurd (heck why not :D )
I once tried quadruple booting Gentoo, WinXP, Solaris and OS X, but the latter two conflicted with each other, so I had to pick one of them at a time.
Try Windows Vista, the worst experience ever. Lol.
I think Minix is a good choice, because theres a new 3.0 version out there.