Fresh on the heals of my recent Mail Sorcery Screencast, I’ve been playing with some other Mail plugins and found this great free plug-in called Letterbox. This plug-in changes the mail view to the Outlook-like side by side view and is very friendly on widescreen macs. I’ve been running a few days and love it.
Have you tried WideMail. I compared both and preferred this to letterbox, although they are both excellent. Just FYI.