The American artist J.S.G. Boggs has become known for his artwork which closely resembles currency. Rather than sell his creations, he attempts to use these bills to pay for goods and services. He doesn't try to pass them off as real, but instead tries to convince vendors that his artwork has the same or higher value as the denomination it is labeled. (Watch a video from the arts show Egg of one his typical transactions.)
Occasionally his work has been seized by the Secret Service but so far he hasn't been convicted of counterfeiting. For more on Boggs, view images on ArtScene or read this entry at Wikipedia.