Cartoon by Randall Munroe
His website: www.xkcd.com. He also has web store.
Creative Commons License
Nick Kim's work includes Astronomy, Alien, Dr. Who and Science cartoons. His website is Nearing Zero.
Space and Alien Cartoons by Australian Mark Godfrey on him smug mug page.
Chris Madden' s work includes Moon, Outer Space and Science Cartoons. He is British.
I enjoy the political cartoons of Cameron Cardow who publishes in The Ottawa Citizen.
T. McCracken has a collection of NASA cartoons and Space and Astronomy cartoons