i hear many good things about FreeBSD - installed it several times and did nothing with it. everyone else i know that uses FreeBSD is practically religious about it

distrowatch.com is a good place to start poking around what is out there for linux. ubuntu and fedora would be my choices

if you are a purist, try gentoo - i hate/love that flavor. you will happily pull your hair out for months getting it 'just the way you want'