"You Thought We Wouldn't Notice" is a blog that calls out artists who slavishly copy the work of other artists.
Todd Goliath [creator of "Boys Are Stupid, Throw Rocks at Them" T-shirt] of David and Goliath tees was recently caught directly stealing art from Dave Kelly (Shmorky on Something Awful). He didn't just copy the image, he traced it! The full story is in the link, there's already a well-dugg article, as well as on Metafilter.
Here are many more examples of Todd Goldman's work presented side-by-side with the nearly identical originals.