Jumping rope is one of the best and most complete exercises around. All you need a medium weight rope...you can buy a jump rope for a couple dollars at many stores. It is also extremely portable...take it anywhere!
Jumping rope does take some practice but once you get into it...you will burn 3x as many calories as running! Plus you can do it for as little as 5 mins and get a good workout. And...you can do it as a family!
Jump rope individually with your kids...have jumping contests (how many jumps in a minute, craziest trick, who can jump the longest or highest). Or jump all together...get a long rope and have two people (or 1 and a fence) twirl and one jump. Want to get fancy...double dutch!