Having just picked up the Lone Wolf Adventure Game, I've become a bit enamored of Jon Hodgson's work. He's worked with Cubicle 7 on Lone Wolf as well as The One Ring game. He also provided illos for the very cool edition of Dragon Warriors produced by Mongoose a few years back.
I find his work to be wonderfully evocative and sometime bordering on the ethereal. The pieces below are some favorites of mine: