R.K.
I am a Black Belt in Tae Kwon Do and I love Martial Arts. Tia Chi, though once a fighting matial art is now a method of exercise and relaxation.
The school I was in taught both Tae Kwon Do (The Art of Hand and Foot Fighting) and Hap Ki To. Hap Ki To is more grappling and take downs, comes in handy for self defense. TKD is 70% feet and 30 % hands, Karate is 70% hands and 30% feet. In Karate you need to be a lot closer to an attacker to be effective. TKD is also considered by the medical community to be an effective exercise program for people with back problems. In order to stay upright while kicking you use your core muscles more, thus stregthening your back. Before you sign up for a school watch a few classes, be sure the instructors explain in detail what the student is doing and how this move works and how you can take a simple movement into a more complicated move as you learn. This should be a part of the class.
I don't recommend just getting a heavy bag and punching or kicking without some instruction. You can break your fingers, toes, hands, feet etc if you don't know how to hit the bag correctly. You will also learn elbow strikes, back hands, and a lot you can't teach yourself. You also learn the pressure points on the body, one light strike on a pressure point can incapacitate an attacker and you can get away without doing permanant damage.
Martial Arts is also a lifestyle of displine and peace. I recommend reading a couple of Chuck Norris' books, no matter what you may think of him as an actor, he is an incredible Martial Artist. Seven time world champion and the first white person to become a grand master in TKD. In his autobiography he talks alot about starting his own school and competing in tournments. And how he got his life together. Looking at him now it's hard to believe he grew up on welfare and food stamps.
Oh, and Happy Birthday Chuck Norris, he's 71 today, I hope I'm in his kind of shape when I'm 71!!!
Good luck and if you need any more info feel free to contact me.