If you have an iMac 21.5" or older 27" screen edition and want to declutter your desk, then the addition of Prism Design's Float Shelf may be of interest to you.
The Float Desk (starting at $75) is made of a heavy (and I do mean heavy) aluminum that matches the weight and texture of the iMac's back screen shell. The edges that will ultimately rest against the iMac's own metal are shielded in a rubberized cover so that it won't scratch either surface butting up against one another.
Affixing the shelf to the back of the iMac is easy. Just position the shelf's cut-out edge along the iMac's base stand and gravity will take over by holding the shelf in place. No additional supports or screws required. Hence the name, Float Shelf.
As you can see by the photo, this innovative design allows for a considerable weight of items to rest upon the shelf. And since the shelf is seated on the outside of the iMac's base, it doesn't interfere with changing the angle of the iMac's display.
If you're looking for an elegant solution to freeing up some desk space while giving your iMac a real-world task of holding your desk items on your behalf, check out Prism Design's Float Shelf on its Kickstarter page for more details.