I did this for my husband's birthday. Absolutely positively 100% analog--no fancy-shmancy Photoshop stuff, for a change.
I used markers, white paint and a bit of colored pencil on bristol. Scary as hell working without that digital net! I tried to keep it really loose, like a convention sketch-type thing. I see a lot of things I would like to fix, and I wish I'd been a bit bolder with color, especially the shadow, but--eh, it's done and he likes it, so I'm happy. :)