Here's some character exploration for a Native American/US Army mash-up. This workflow (from drawings to value studies) is typical of the way I zero in on a character design before committing to a final color render. I'm always attempting to provide myself with as many options as possible along the way.
Although most of my published work tends to take the form of a final illustration, there's a great deal more along these lines. I find this to be some of the most gratifying work there is ... when the character is still rich with possibility and every line makes a difference. This approach is particularly useful in a studio environment where these sorts of sheets hopefully generate a lot of conversation and reveal any number of potential directions the character could take.