Microsoft has released the latest updates for Office 2008 and Office 2004, to address a critical security issue in Excel and improve performance. The 2008 update requires you to have installed update #12.1.0. If you're using MS Office for Mac 2004, be advised that it will cease to be supported as of as of Oct 13, 2009, and will thus no longer receive any updates.
(Source: TidBits) | Cost: Free (update) | Requires: Mac OS X 10.4+ | For further info...