-George Lucas = star wars. Not an artist, but thanks to him every time someone with little knowledge about sci-fi sees a drawing of a spaceship: 'that's so star wars'. Not sure this counts, and there are hundred of artists that make star wars what it is.
-Sparth, well mainly the steambot guys. mastering speedpainting and random shape photoshop brushes
-Ryan church, worked on so many hugely important titles, i think his work is of great importance. His Gnomon Dvds are excellent too
-Feng Zhu, I'd say. Who doesn't know him? his style is immensely inspirational to many many artists. he did the concept design dvd series. his thumbnailing teechnique is great. i don't know if he invented it, but it's more or less the techniques that were used in "the skillful huntsman" and "in the future" by designstudiopress
I'm far from an authority in this area, but the first name that came to my mind when seeing this topic is Marko Djurdjevic. Why, even this morning I was looking through some sketchbooks and thinking, "Those character designs have obviously been influenced by Marko Djurdjevic."
Disney-which had the earliest concept art positions listed that I can find. It starts with those old masters there.
Mead- Where would we be without the old master himself?
Mullins- He leads the industry. Always. Back in the say, people said he was great at landscapes and environs but needed to work on his figures. No one would dare say that now. Seriously, one of the best who ever lived. Is perhaps the most peer admired concept artist in the history of the field.
Justin Sweet- Whom art directed Puddnhead, myself, Android, Vance Kovacs, John Dickenson, and others at Black Isle Studios. He was one of the best when we entered the industry and was a master of digital painting by the time any of us began to use a wacom.
El Coro- No one has done more concept art in the games industry than this guy. I have yet to find anyone in this industry with a stronger back for heavy lifting and team leadership at the same time. And, he has led, and leads, the team that has done more game concept work than any other in the history of the industry.
There is a tie for the other with about a hundred other names. The games industry concept folks are thriving nowadays. I am inspired by a ton of folks. I think we all are. There are the UBI/Steamboat guys, the id software guys, ArenaNet guys, NCsoft guys, Star Wars guys, Sony, you name it...there are a ton of influential artists working today. I am glad to be a part of it, even if just a little bit as a facilitator...the other guys are the leaders...not me. I'm just helping out.