Did you make a New Year's Resolution to get moving? Consider studying Aikido.
Aikido is a traditional Japanese martial art that places a great deal of emphasis on the mechanics of motion. Aikidoists do not punch or kick opponents, but instead employ joint locks, pins, and unbalancing throws that use an attacker's own mass and motion against them.
Aikido does not depend on strength for effectiveness and can be practiced by individuals of all fitness levels. It helps improve stamina and flexibility. As with all martial artists, there are also self-defense applications. Plus, it's just plain fun to do.