Ballet! =D I started doing ballet warm-ups a few weeks ago after someone told me I had Dancer's Legs (I wanted to live up to that name!) And although it hurt like heck for the first few days after a while it stopped hurting, my legs grew stronger, I swear my butt looks thinner now (=D) and best of all it calms me down.
Ballet demands some form of discipline. You need to keep your head up (Or down depending on the move) straight, back straight and firm and be sure not to lean when you move your leg or something. Now trying to concentrate on all that is hard, but good. It just takes you away because you can't be worrying about whether or not you need to call some dude tomorrow while trying to do a.....*Doesn't know how to spell it*
I also highly recommend Yoga! Everyone knows it's relaxing! (But don't do it in a group because all the stretching sometimes causes people to pass gas ^^) I wouldn't recommend you do Yoga and Ballet at the same time. O.O Because it would hurt....a lot. At least until you're ready. Once you're physically fit you can work for hours with no rest or pain. I can only make about 1/2 an hour now but it's progress! Good luck.

Love Jen