I like the way bumptop organizes file stacks (similar to "stacks" in the dock, but more flexible)--though the jury is still out about whether it will improve my productivity or not.
Below is my 3D desktop using bumptop. The stacks of photos are there for illustration, but the video at the bumptop webpage shows how you can sort and scrub through stacks of documents/photos. Notice how you can post links, pending documents, and sticky notes on the 4 walls (the back/bottom wall is not visible unless you navigate to it). You can also switch to 2D mode on the fly.
This really works well in conjunction with expose, spaces, and fluid for Mac (used to create websites as applications). The multi-touch gestures on the MBP are really what make the program useful, but we'll have to wait and see if they expand the functionality in the Mac version to match their Win7 version.
While we're talking about OSX...here's a great tip recently posted on MacOSXhints.com to enable tab completion in Terminal for SSH hosts via this in your .profile: