I am a big fan of Alex Ross' work. Everytime I see a comic he worked on for sale, I grab it. It is more of a water color look, but he goes to great pains to make sure the shading and color are closer to "real" (or what passes for real in the comic world). He has 2 sites that I know of. Unfortunately, neither of them have tutorials, but they give a great example of his style, and as was mentioned above, sometimes just using it as a reference is a great help.
This is his main website (unless there is another I am unaware of) and is currently showing his JLA: Liberty and Justice work:
The next one is not so much about his work, but an auction site he runs (I think) for original work by other artists. I post it only because some miht find it useful for reference purposs:
Hope this is helpful. Thanks to our ever-faithful mod for a great idea. :thumbsup: