If you are really interested at getting to the core of things, Aikido, BJJ, Krav Maga...no matter...i'd take a look at some of Tony Blauer's stuff. We are using it in the Army to a degree (coupled with other methodologies of training).
Worth watching this one, and a few others if you are interested in true core of reality, and developing good, sound, basic instincts that are tactical.
http://www.youtube.com/watch?v=jk_Ai8qT2s4