Microsoft-provided removal tools for Office. A new page for 2007 through 2016:
Fix-Its now exist for Office 2010, 2007, and 2003:
http://support2.microsoft.com/kb/971179
A utility for manual removal of Office versions at and before XP, is reportedly in the 2003 Office Resource Kit, confirmed available at the link below as of right now, although the installer appears to crash:
http://download.microsoft.com/download/0/e/d/0eda9ae6-f5c9-44be-98c7-ccc3016a296a/ork.exe