UPDATE: Updated for Snow Leopard Launch!
When Mac OS X Leopard shipped, it included some gorgeous illustrations of Apple’s Mac line-up that display in the “Shared” section of Finder’s sidebar and when looking at “Network” in the Finder. A Cocoa application can also take advantage of this resource for representing your machine in its interface.
These icons are hidden amongst the System Library shipped with Leopard. The folder they reside in is easily accessed by launching Finder, selecting “Go”, then selecting “Go to Folder” and entering in the following string:
/System/Library/CoreServices/CoreTypes.bundle/Contents/Resources
All the icons beginning with “com.apple” are the Mac models that Finder recognizes (you can see them in Cover Flow or by launching them with Preview). Pretty, right? The only problem is that the Macs with built-in displays have a blue Tiger-style desktop picture.
It might seem a little late with Snow Leopard’s launch just around the corner, but I have no clue if Snow Leopard will fix this issue. So I spent a little time grafting the default Leopard desktop picture to all the Mac models with displays. This persists even with the launch of Snow Leopard and new Mac Models.
Here’s a preview of what my Finder looks like after changing these icons:

Finder Sidebar

Row of prettier Macs
I really do want to make an app like mimiFoto that modifies all of these icons. If there is enough interest, I’ll definitely look in to it.
But for the time being, I’m sharing the updated icons so that they may be installed any Mac with Leopard right now.
Installation instructions:
Copy/Paste in the following string into the text box then click “Go”
/System/Library/CoreServices/CoreTypes.bundle/Contents/Resources
Create a backup of this folder (in case something goes wrong)
If there are shared Macs on your network, Finder’s sidebar should be looking more purple. If you have any trouble, hit me up on twitter: @kennardsmith