All Mac notebooks, iMacs, and Cinema Displays have horizontal widescreen displays. However, Mail, the email client built into Mac OS X, has a decidedly narrow interface by default. I find this rather awkward; I prefer a three-column email interface, with mailboxes, inbox, draft folders, etc in the left pane, new and unfiled emails in the center pane, and the email itself on the right pane. This makes it easy to scan my inbox as well as read email messages.
Back when I was still using Tiger, I used the Letterbox plugin
to get widescreen Mail. I loved it, but it no longer worked when I upgraded to Leopard.
Fortunately, I discovered WideMail while surfing Macupdate. WideMail is a plugin for Mail for Mac OS X 10.5 Leopard that turns the message view from a two-row horizontal view to a two-column vertical view.
I’ve successfully used WideMail for about three weeks on all of my Macs. If you have Leopard, read more about the plugin and download it here!