Running comes in at the very top of our list.   Although there has been plenty of
  debate surrounding whether or not fast walking burns the same amount of calories
  as a slow run.  Well, the results are in, and running at least a 10 minute mile for
  30 minutes will burn 395 calories.

  Of course, running a faster mile will increase your calories burned per hour.  Those
  who ran a 7 minute mile burned up to 260 more cals per hour.

One of the most intense and thorough aerobic workouts, jump rope burns up to 360 calories per half hour.  Not only do you get your cardio, but your calves,
quadriceps, biceps and triceps also get a workout.  The most effective way to
jump rope for a good calorie burn is to do the single rep jump, where both feet
touch the ground at the same time and lift back up immediately without a rest
(that little double bounce that you see some people do).  Eliminating the double
bounce burns nearly twice the calories.

A complete body workout that can be both aerobic and anaerobic, depending on how
intensely you train, kickboxing (hitting mitts, the heavy bag, and/or sparring)
for a mere half hour can burn up to 380 calories.  A thorough kickboxing work out
typically lasts a bit over an hour, between jumping rope, shadow boxing, kicking and punching warm up drills and then bag work.  So, on average, figure that you're really
going to be burning anywhere near 800 calories per hour with this work out.

Definitely not for the faint hearted, a good rock climb will put your entire body
to the test, most especially your arms, shoulders and core.  A half hour of rock
climbing will burn roughly 400 calories. 

Given the high amount of exertion needed to pull oars through the resistance of water, a real canoeing can burn 380+ calories.  Your entire body will be worked from head to toe here.  The gym rower can get you about 75 to 80 % of the same intensity and calorie burn.  At the gym, you will have to put the resistance up high
and work vigorously to even nearly match the same effort needed in a real boat.

It's absolutely true what you've heard about cross country skiing.  It is indeed
one of the most intense workouts on our list.  This activity has been known to
burn up at least 360 calories per half hour.  Also, the fact that your clothing
will be a bit heavier in this climate, your body temperature will also rise a bit
higher during a brisk cross country ski, thus increasing your calorie burn.

Racquet Ball

Grab your racket and hit the court!  This activity can burn up to 420 calories
for a half hour of play.

Step Aerobics

Depending on how many risers you use during a class, step aerobics can burn up to 800 calories per hour.
This was calculated using one riser underneath the step.  Increasing it to two can up the calorie burn nearly 35%.

Water Polo  (supposing you can find a pick up game somewhere...)

Water polo, a game that is played while treading water in the pool, requires a huge amount of energy and stamina.  Having to move through the resistance of the water makes it a great combination of an anaerobic and resistance workout.  You will burn up to 400 calories per half hour here.

Interval Training

Touted by many fitness professionals as the best of the workouts, interval training can burn up to 400 calories per half hour.  Intervals can vary in length from exercise to exercise.  Most include intervals of an exercise at one level of intensity for a few minutes, followed by a few minutes at a different intensity, and you switch back and forth.  You can also combine types of exercise intervals, mixing in cardio segments with weight training, and/or plyometrics.  The average interval training session can burn anywhere from 700 to 900 calories per hour..

So, go ahead.  Choose your weapon, and let the calorie burn begin!