Server: CentOS. A completely free rebuild of RedHat Enterprise Linux. A good, stable, usable system perfect for a server. Doesn't have all the latest apps like Firefox 3 or Gimp 2.4, though.
Desktop: KUbuntu. Built on Debian goodness, with KDE as the environment. Easy to add all the latest bits, with plenty of repositories even for "non-free" components like mp3 players.