Interestingly enough, talk to any Ninjutsu practitioner worth his or her salt and you'll discover they don't generally take stances per se; it's more like transitions in footwork, to which names were given to those 'transitions' that were used a lot. An example is Shizen no Kamae (kamae is Japanese for 'stance', but is better translated as 'attitude'): stand with your feet shoulder-width apart, relaxed but alert, back and neck straight, and weight evenly distributed. Note how this is also basically one's everyday posture. The ninja incorporated this into their art since they figured it was in this posture they'd get attacked most often.