Ryan Church is about as close to the top of the concept art world as you can get. He's worked on Star Wars movies. He's working on the new Star Trek movies. He's worked on Avatar, Transformers and John Carter.
In addition to all that movie stuff, though, he's also found time to lend a hand in the creation of a number of high-profile video games, like Dead Space, Red Alert 3, Battle for Middle Earth II and the cancelled Steven Spielburg project, LMNO.