Spambayes (Windows)

Spambayes is available free of charge and is the best program we have found to deal with spam on your computer.
Information about spambayes and downloads are available at http://spambayes.sourceforge.net

SpamSieve (Mac OSX)

SpamSieve is available to filter mail on Mac OS X systems.
This program can be downloaded at http://c-command.com/spamsieve
Information can be found at http://c-command.com/spamsieve/manual