One could conceivably create an artwork out of any office item imaginable - pencils, paperclips, staples etc. but it seems the most popular is the post-it note. This photoset on Flickr demonstrates the point in hand, the square shape of the post-it in this case being a substitute for a pixel with the iconic images of an enemy from the popular arcade game Space Invaders and The Mona Lisa being given the 'office art treatment'.
As a couple of small project these are pleasing on the eye, maybe due to their novelty and almost definitely because of the flourescent hues. They have an appealing spontaneous quality in that these were probably created one lunch break when the boss wasn't there.
Aside from this it's a basic idea but it works. This is often the best formula for success.