Jim Moore is a professional science-fiction concept artist who has worked on some games like Dead Space 3. His professional art blog can be found here and it has some impressive work.
My favorite thing about Moore is his vivid imagination in world creation. For both sci-fi and fantasy settings, he uses bright colors and utilizes this great pairing of whimsy and sobriety in his work. Much of the sci-fi artwork can have a sterile or mono-chromatic feel, but Moore’s comes bursting with color and bright spots amidst the darkness. His use of light is integral to that process and it’s quite stunning.