One of my favorite workouts has to be Martial Arts training. This is a simple but effective way of burning some serious calories and staying in great cardiovascular shape. If you like learning martial arts and different styles I would recommend learning Capoeira. I have recently started Capoeira and within the first ten minutes or so of constantly moving around I break a pretty good sweat.
Capoeira is very different from a Chinese of Japanese style of martial arts. Your fighting stance is not stationary but it is always moving (this is called the ginga). From there you learn all sorts of kicks, escapes, dodges, and (if you want to) some aerial moves.
I would highly recommend Capoeira to anyone who likes to constantly move around and is looking for a replacement to their old cardiovascular activities. However Capoeira is very technical and it will take lots of practice to get the moves down correctly. I recommend finding a trainer who can instruct you, but if you don't want to spend to money and learn on your own like I do here is a fantastic website for you.
http://www.capoeiranation.com/
watch this video for a Capoeira demonstration
