Tai chi short form is excellent as a fitness regimen and is kinda like meditation for the body as well as the mind. The principles of balance and directing energy in "slow motion" kinda appeals to me.
I dabbled a bit in hapkido as well with an emphasis on self defense techniques; grappling with a lot of traps and joint manipulation. It doesn't require a lot of strength to take down someone if you grab them the right way or know how to react to how they grab you. And the end result can be rather crippling.