Mailwasher - Over 8 million people use MailWasher as their spam filter
Zenity - Zenity is a tool that allows you to display GTK dialog boxes in commandline and shell scripts.
SPAMfighter - SPAMfighter and Microsoft have built the strongest and most effective anti spam filter for Outlook, Windows Live Mail, Outlook Express & Thunderbird
Glade - Glade is a RAD tool to enable quick & easy development of user interfaces for the GTK+ toolkit...
Spam Reader - Spam Reader is a free anti-spam add-on for Microsoft Outlook.
Yad - Yad (yet another dialog) is a fork of Zenity with many improvements, such as custom buttons...