I think the Israeli martial art of Krav Maga is very effective. I have trained in this art and found though that while it is great for younger people, it can be a little hard on the body, and in time may introduce limitations.
I am currently studying Systema, it is a Russian Martial Art used by some Special Operations. Systema has a nice balance of soft / hard principles and teaches ones body to repond to any scenario and not just react with techniques.
As it is not well known, schools can be hard to come by. Anyone interested in checking it out should go to
http://www.russianmartialart.com/ for more info.
Cheers.