One of the Outlook views I sorely miss when on my MacBook Pro is the three vertical column view. It’s a personal preference to be sure, but I like having my folder list on the left, Inbox flowing down the middle and my preview pane on the right… especially when I’m using a widescreen monitor. SvenOnTech turned me on to Letterbox, a free Mail.app package that gives me this view on OS X.
I grabbed it last night and used it happily throughout the day today. On a smaller screen, say the 13.3-inch MacBook, I might opt for the standard view that puts the preview pane under the mailbox contents, but Letterbox is great on my 15-inch MacBook Pro and on the 24-inch widescreen external monitor I have connected.