David A Hardy is a space artist. His AstroArt homepage has galleries of art done for science fiction magazines, book covers and commissioned material. Landscapes with two suns, planets with rings, spacemen and the such. Fantastic. My favourite includes a dinosaur, as all good illustrations do.
Another sci-fi artist: The Chris Foss Tribute Page has tons of scans of the airbrushed spaceship pictures that covered most of the books I had when I was a kid.