Another vote here for Ubuntu, using it at the moment, and have had it on my server PC since the 5.x releases (used to use Fedora/Red Hat before that, then Mandrake before that, and originally Slackware).
Great OS, fantastic "one-click" repository of tonnes of software, and the multimedia CODECs, etc, are just a few steps away (search for "Automatix" and "Easy Ubuntu" for scripts that install the essentials automatically - including the multimedia stuff, wine, Acrobat Reader, RealPlayer, DVD player, etc).
And coupled with the free VMWare Server, it makes a great AROS testing platform!
- Ali