UPDATE: I figured out how to get the 2-line message list view working and have added a screen of it below. It is really sweet.
Kevin recently turned us on to the great Apple Mail plugin Letterbox and I installed it immediately and loved the 3-pane display. Reader Clayton Lai commented that he preferred Widemail and I gave it a try this morning and it is awesome! Widemail gives you a 3-pane window in Apple Mail like Letterbox but allows you to completely control the formatting of the display. It also provides two useful settings, one lets you put the email preview pane below the message list which is my preference and the other lets you display every other line in the message list in a different color. This makes it a breeze to review folders with a lot of mail. Here’s a couple of screens showing the preview pane on the right and below the message list:
Both screens show the message list with every other emal in blue. Widemail is our Mac Freeware of the Moment so enjoy.