Mozilla has just released version 2.0 of their Thunderbird email client. Thunderbird is a free, desktop email program that features a small footprint, customization, and some smart ways to stop junk mail. New features include an new look & feel, message tagging, improved and savable searches, and easy integration with web based email accounts such as Gmail.
You can read my review of Thunderbird 2 here.
Update: If you would like to try Thunderbird 2.0 without affecting your existing version head over to Portable Apps and download the Thunderbird Portable 2.0 Pre-Release version.