Over at Instructables, Lifehacker reader Matt Lumpkin has posted a detailed guide to how he mounts his laptop on the back of his monitor for an iMac-like all-in-one PC. Obviously this isn't limited to Macs, but if you want to save some space, declutter your desk, and create a nice, clean monitor-only look, the results speak for themselves. The idea and setup is incredibly simple.
Matt's taken a mesh-wire file rack and screwed it onto the back of his monitor. Clearly you'd need to be very careful setting this up (a screw through the front of your monitor would be awfully distracting), but if your monitor can support the weight of your laptop, it's a pretty cool way to get the clean simplicity of an all-in-one monitor and PC.