Elite: Dangerous has an excellent array of stunning artwork which started life as concept art in various guises. Below are some images and links (click on the artists names) to various pieces of work designed for the game. Copyrights as per details in links. Note: Some artwork does not necessarily reflect the final in game assets.
Originally promised as a reward to backers this pdf features some superb artwork stretching back into early development, right up to some art for future additions to the game.