So you have a Mac with a widescreen...
and want to make the most out of it. Well, two of my most favorite apps that I use daily are Vienna and Apple Mail. In Vienna (most people probably already know) you can go to "View" -> "Layout" (in the menu bar) and change the layout to condensed to get out most of your widescreen.
In Apple Mail however, there is no built in option to change the layout so that it fits the widescreen format. Well, there is still a very nice little plugin called WideMail that you can download and once properly configured your Apple Mail will look like this.
I have to say wide is just more beautiful;)