What is some fun, free exercise?!

I prefer the latter....

Anyways, crank up the music and dance! Just go crazy! It helps if you're in some ridiculous whitey tighties too.

Jumping rope allows you to have a quick, efficient workout in the
privacy of your room. The jumping rope itself you can buy in a dollar
store for about 50 cents. You can exercise in front of your TV.
Jumping is more efficient that jogging, and burns more calories. It
does not require a lot of space. It builds up your strength, tones
your whole body, build legs muscles.
People who used jumping rope reported significant results after one
week of exercising.
When jumping rope it is important to remember to not push yourself
too hard. Just because children jump rope doesn't mean you can't over
do it. Begin with about twenty-five jumps a rep, with a rest between.
Gradually shorten your rests as you improve, but it is not advisable
to cut them out completely due to the high impact nature of jumping.
Before you begin a jump roping work out, you need to be familiar with
the basic jumping techniques. Begin all jumps by holding the rope
handles at your sides, with the middle of the rope at your feet.
Basic Jump
Begin with rope behind you. Swing rope over your head, moving hands,
and rope, forwards. Jump over rope with feet together.
Reverse Jump
Begin with rope in front of your body. Swing the rope backwards, over
your head. Jump over the rope just as you would forwards, keeping feet
together.
Jogging Step Jump
Begin as if you were doing a basic jump. When you swing the rope over
your head, do not keep feet together. Instead, switch them back and
forth, in a jogging motion as you jump.
Criss Cross Jump
Begin as if you were doing a basic jump. When you jump over the rope,
bring your left arm over to cross the right. Then bring arm back over.
Twisting Jump
The twisting jump is simply a basic jump, but as you jump, twist your
lower body side to side.
Double Under
When you have had some practice jumping, try to move the rope twice
under your feet for each jump. With even more practice, you could even
get it three or four times under.
After you have mastered the jumps, you can combine them to create a
fun, challenging workout. You can also jump in different ways to keep
your work out interesting. For example, you could do what is called
square jumping:
Use tape to make a square on the floor, or use chalk if on concrete.
Then, divide the square into quadrants. Then, jump around into each
square in a clockwise, then counterclockwise, direction. Begin with a
basic jump, and then add whatever jumps you wish.
Another thing you could do is try to move a set distance while you
jump. You could hop forward each time you did a basic jump, or do a
jogging step jump, but move forward instead of remaining stationary.
If you do not have the room available, you could do this in a circle.
Alternating legs is also a very good exercise. Try doing ten jumps on
your right leg, then ten on your left. Balancing while standing with
upright posture during this will help to tone your core muscles, and
helps your body all over.
The most important thing is to have fun. Any exercise that keeps you
from being bored will keep you exercising. If you find things getting
a little dull, mix it up again. With jump roping the possibilities are
infinite.

A Kinect is a really fun way to exercise. http://want-2-b-healthy.blogspot.com/201… Of course it's not free to buy it, but it's free to play once you have it. Does that count?

I enjoy using mine a lot and it's pretty good exercise. I'd recommend Dance Central.