Nowadays, if you want to have a 3D desktop, there are quite a few choices. I will talk about the three main ones I have tried here.
3D Cube desktop - there are many implementations of these, Yodm3D being the most popular. It provides you with four faces of a cube to work on, and you can have one wallpaper on each face.
360Desktop - this project is still in beta, but it seems quite functional. Your desktop can truly become a panorama, and you can have webpages displayed directly onto any part of your desktop just like with the old Active Desktop. (This is, by the way, the only way to have active desktop functionality in Vista that I know of).
BumpTop - this one provides you with a simulated real-life desktop. It is ideal for desktops with lots of documents, as you can pile them up and sort them out easily, like you would do on a real desktop.
Another program I would like to mention is Madotate, which allows your windows to lie in 3D positions whilst they are inactive.