Just saw this on 9to5mac and TUAW, and being the big Facebook fan that I am, wanted to share it. I've been using Amigo for a long time, but this looks to be a decent improvement.
[Link to Facebook app]

In order to promote the Facebook obsession, developers there are now building a Mac app that offers Desktop Notifications. This inhabits the menu bar at the top of your screen and lets you access your News Feed, recent Wall Posts, and messages. And it’s available now for download, though the company is warning that this is just a protoype.
[Link to Facebook app]