Here is a little feature of Kuen Ju Kim, aka Skipio and his character concept art. His blog may be all in Korean, but his site, rabbiteyes gives us a gallery of pieces to draw inspiration from. His gallery shows off a range of sketches, finished pieces and concepty bits. I think he does a great job of injecting something gritty into the stylish almost cartoony characters.
I love the silhouette-like character study images – very cool. Check his site for the many more and at full res, here are a few to lure you that way: