Photoshop. Photoshop 7 to be exact. Vector art is much more practical through Illustrator, the way I do it isn't necessarily the 'best' way, but I've been doing it like this for 6 years. Old habits die hard I guess. I get a palette worked out, then I start building the image out of shapes using the pen tool, overlaying some over each other and others under, kind of like weaving.

Thanks. Great work btw