James Charles, in his series American Iconomics. used real U.S. currency for each of these drawing of American icons.
Pop-Art Portrait Paintings on World Coin
Brazilian artist Andre Levy miniature portraits on coins of pop-art and pop-culture figures from Major Lazer and David Bowie to various X-Men and Thunder Cats to Finn from Adventure Time and Legolas from LOTR in his ongoing project.
See also Alien Nickels
The Evolution of the $100 Bill
The US $100 bill from the pre-1860s to the newest of them.
Currency Collage: $1 Bill
Mark Wagner makes these stunning collages out of $1 bills. Be sure and check out his mega-collage called Liberty.
From the Artist Statement:
The one dollar bill is the most ubiquitous piece of paper in America. Collage asks the question: what might be done to make it something else? It is a ripe material: intaglio printed on sturdy linen stock, covered in decorative filigree, and steeped in symbolism and concept. Blade and glue transform it-reproducing the effects of tapestries, paints, engravings, mosaics, and computers—striving for something bizarre, beautiful, or unbelievable... the foreign in the familiar.
3 - Alien Nickels
We've seen hobo nickels before with their amazing skulls and whatnot. These alien head nickels... yeah, let's start a petition to get these to be legal tender, yeah?