Note: Face2Face is no longer for sale. Its functionality is now included in Feigeist's MailButler, whose link can be found int he following paragraph.
Face2Face--which is now a part of MailButler, the complete assistant for Apple Mail--adds new image sources to Apple's Mail application. These images are received from Facebook, Gravatar or Face2Face's own image database. With Face2Face you can see who is sending an email and have a more personal email conversation with somebody.