I think Bill Watterson's Calvin and Hobbes was a great contribution to contemporary art. Hardly any filmmakers or musicians have added so much joy and understanding to my life as watching Calvin play games with his stuffed animal that came to life in his imagination. (Or was it real? I choose magic.)
I was happy to stumble upon an online collection of Watterson's other work; I had seen a few of these here and there but never found them all together. It includes strips he contributed to his college newspaper (which include characters that look strikingly like Calvin's parents) and bits of work from other parts of his life, such as artwork he made for his brother's band. You can check it all out here.