I've heard good things about interval training and swimming. Interval training uses the element of 'surprise' on your body. I've read many articles about interval training and i'm sure i could find you one (sorry, my net's capped atm )
Skipping is a good fat burning cardio workout and also you might notice that your calf muscles start to develop more. Win win to me
Swimming is generally a really good cardio workout though, your whole body is used effectively and your breathing will increase etc
I don't know if you have tried running first thing in the morning (no breakfast) around the block, but that might work for you.
Skipping is awesome, once you are at the level where you can go for 30 minutes non-stop the amount of calories you burn is huge. Defiantly one of the top ways to strip body fat fast!