I can already hear the groans just from reading the title.
Don't worry, I'm not going to tell you to put on a pink tutu and have you doing splits, unless, of course, that's your thing.
Ballet isn't all twinkle toes and limp hand gestures, and if you don't believe me, try some of these ballet exercises.
Be sure to warm up properly first on an elliptical or other low-stress machine to get your blood flowing and body as limber as possible.
Ballet Exercises

• Plie- You are probably thinking this is just some crazy squat with no weight that's going to look ridiculous.
  In a sense, you are correct.
  Stand facing a wall an arm's length away, feet together and turned out.
  Only turn out as far as you naturally can.
  Lift from your abs, and tuck your glutes (don't squeeze).
  Finally, lift your shoulders up and back, keeping your neck in a straight line.
  Now simply do a squat keeping your body in a straight line.
  Squat all the way down so your heels come off the floor, but you shouldn't be sitting.
  Then come up pushing your heels down and lifting from the top of your head.
  One movement should take about 8-1-0 seconds.
  
• Battement- Assume the same position as before except stand facing at an angle to the wall so you can kick forward.
  Essentially all you will be doing is kicking.
  Simply keep your legs turned out and brush your foot up keeping it straight until you cannot go any higher, hold and bring down brushing the floor back to the starting position.
  Your upper body should not move; it should be a slow smooth motion taking about 6-8 seconds.
  Repeat on your other side.
  
• Releve- Take up the same position as in the plie, facing the wall.
  Now just do a calf raise, but again staying lifted in the abs and tucking the glutes.
  Lift through the top of your head.
  This movement from start to finish should take 5 seconds.
  

These simple ballet exercises help develop muscle control because of the amount of time that each movement takes.
Just take a look at the physique of some male ballet dancers to see how demanding ballet can be.
It also helps your diaphragm learn proper breathing technique because you should always be breathing out when doing an up motion and in on a down motion, there should be no pause.
Finally, doing these over a period of time will make your legs look defined and tighten your glutes.
Just make sure when you have finished these to hop on the treadmill or take a walk around the house to cool down.