Spamihilator - The free Anti-Spam-Filter Spamihilator removes more than 98% of spam mails before they even get into your inbox.
MailStore - MailStore Home - A 100% free single-private-user desktop solution
SpamAssassin - Use this program to "Unspam" your mailbox(es).
MailSteward - MailSteward : The Ultimate E-mail Manager for Mac OS X
Spam Reader - Spam Reader is a free anti-spam add-on for Microsoft Outlook.
Gmvault - Backup the emails in your Gmail account.