I did Judo, Aikido and Karate in my younger days. Of those, I would recommend Judo first, because it\'s good excersize, felixibility, and usefullness (how to fall, protect your head, hold/pin, throw).
I\'ve branched into boxing in recent years, which is I think far more practical as a purely fitness building sport, but can lead to a lot more bulk if you train a lot.
The skills you learn in boxing you never forget, and it\'s nice to know you can take a punch and protect your head/body.