IotD always enjoys art of the commoners, and there isn't anything much more common than your basic cardboard beer coaster.
This bar in Spain has accepted a collection of artistic works involving cardboard beer mats, which leads to their
online gallery of submissions, a webpage that scrolls entirely horizontally. Sure, I hate that too, but the gallery is interesting and I guess you can think of yourself as walking down the bar to look at them.
The above item is from that exhibit, an entry from Argentina. Many of the other entries are much more involved and sophisticated, but even the simple pen and ink stuff is highly stylized and fun to look at.