I always like poster art. In particular, I like the way poster artists manage to make such effective use of a limited color pallet. Several of these are excellent examples:
[Update 2016-02-14: That link seems busted, but a search still finds the exoplanet posters: http://www.chungkong.nl/?s=exoplanet]
With just a few shades of the same color, the Chungkong paints a whole alien world.
—via Jay Lake.