Johan Wahlbäck, featured on Kotaku.com, is a concept artist who works for Southend Interactive and has contributed to art on the game Bloodline Champions, amongst others. Something I really admire is his ability to effortlessly shift between styles - sometimes his work is graphical with strong lines, more suited to cartoons; other times it is highly detailed and realistic.
At his portfolio site I browsed through his work, which ranges from silhouette sketches to weapon concepts, to completed illustrations. Something I'm particularly noting is how he expresses initial ideas for concepts in ways that are easy to understand. (A problem of mine is that all my sketches tend to be messy sometimes to the point of being incomprehensible...)