Who says you need expensive materials to make art? Other than a somewhat flat surface, all you really need are a few hundred Post-it Notes. The colorful squares are practically screaming to be made into mosaics, aren’t they? More than a few people have certainly thought so - here's some prime examples:
This piece was done by Illegal Art, a New York public art collaborative. The blank Post-its were carefully placed and strangers stopped to write their To Do lists on the notes.
Nintendo played with the concept when they promoted the Virtual Console, a way to download old-school games right to your Wii. Pretty smart.
This self-portrait by David Sieren is amazing.
You can check out more Post-It Art on this Mental Floss post.