Official Ubuntu Server Book, Kyle Rankin & Benjamin Mako Hill, if you want something in paper to skim, and something you can often find at Barnes & Noble if you

Official Ubuntu Server Book, Kyle Rankin & Benjamin Mako Hill, if you want something in paper to skim, and something you can often find at Barnes & Noble if you want to grab locally, (or of course you can Amazon it) 2nd edition, copyright 2010, covers 10.04 LTS; the 1st edition copyright 2009 covers 8.04 LTS.