Mailwasher - Over 8 million people use MailWasher as their spam filter
SpamAssassin - Use this program to "Unspam" your mailbox(es).
Spam Reader - Spam Reader is a free anti-spam add-on for Microsoft Outlook.
SpamSieve - Save time by adding powerful spam filtering to the e-mail client on your Mac.
POPFile - POPFile classifies email into categories you define.
Spamfence.net - Professional e-mail security free for private use: With Spamfence.