I've often wondered what would be a good, all around type of martial art to learn that would suit the needs of an average joe like me on the streets.
Over at Hell in a Handbasket, James suggests boxing, as it is easy to learn the foundation to make for useful combat; even against multiple opponents, which is what my main concern would be. He has a very compelling video on that post that stresses his point. Go check it out.
Violent scumbags generally work in multiples, so a single based approach to empty hand techniques would be training to fail in my case. Also, I'm the exact opposite of flexible, and any attempt for me to do a ninja roll would result in torn things inside my body. While I'm sure you have to be limber, boxing doesn't look like it focuses on the more complex techniques that will require a greater deal of flexibility.
I will have to look into boxing in the near future.