If you belong to a gym or the Y- you can play racquetball on their courts and if you don't own a racquet - you can sign one of theirs out to use.
And even if you don't have anyone else to play with - you can play all by yourself and actually that's a really good workout and FUN! If you have to return every ball you're running back and forth twice as much and it works all your muscle groups - legs and arms- while also twisting your torso so it works your waist too.
It'll get you ready for tennis too - in terms of improving your hand-eye coordination and facility with the racquet.
I also really like to rollerblade- that'll work your legs, hips, and butt. And again, it's fun - you can do it all by yourself and there's no expensive equipment to buy (just skates).
And these are both things you can do for the rest of your life - I've been doing both of these activities since I was ten or twelve years old.