I learned of James Gurney after stumbling across his blog around six years ago. He makes a very strong effort to show his work in it's various stages, from very rough to simply beautiful. He doesn't try to hide his process -- he tries to be open and forthcoming, two qualities that attract me to the ideas encompased by "open source."
His work focuses on two areas -- "Imaginative Realism" (realistically painting things that don't have any full references, like dinosaurs) and "Plein Air" (essentially going somewhere and painting what you see).
His preferred medium seems to be watercolor, gouache (kind of an opaque watercolor, but not really), and, lately, casein (milk based paint popular prior to 1960, when acrylic based paints gained popularity).