Worried about burning up fossil fuels while you're out enjoying the water on your jet ski? Ditch it and pick yourself up an Aquaskipper ($500). Powered by your own "hopping" motion, it allows you to get some exercise as you propel yourself across the water at speeds of up to 17 miles an hour. The 'skipper is big, but since it's made of lightweight aluminum it weighs only 26 lbs., making for easy assembly, disassembly, and transport to and from the water.