Some more very cool illustration design sites that I've found and love: hip.young.thing. This website profiles art, design, fashion, etc. and is updated really often. There is such a huge variety of really cool things on there.
ghostco I really love this guys illustration - he is very amazing. I find his skeletal work especially interesting, as one of the papers I did at uni was just focussed on skeletons, muscle structure, then skin/outer layer. I love the way he makes each layer see through, so the structure is visible.
Emil Kozak This guy is awesome - he's a designer and artist and he's done artwork for skateboards, etc. etc. I love his stuff :-)