1. Swimming: The water doesn't just cool you off: It provides full-body resistance you don't encounter on land. Your arms are key for propelling you forward, so you'll sculpt strong, sleek swimmer's arms while burning as many as 680 calories an hour.
2. Cardio machines with movable handles: Focus on pushing and pulling with every stride. Start by doing 1 minute with arms/1 minute without, and gradually increase. If your machine doesn't have handles, bend your elbows and pump your arms as though you're power walking.
3. Rock climbing: Grasping overhead handholds gives your upper body a fresh workout, and you can blast up to 750 calories an hour as you figure out the best route to the top. Find indoor climbing facilities nationwide at indoorclimbing.com.
4. Kickboxing classes: Throwing punches and jabs is a great way to get your heart pumping and melt up to 680 calories an hour. Get two free 20-minute routines to try at exercisetv.tv (just click on "kickboxing").
5. Canoeing or kayaking: Paddling down a river is the perfect family adventure, and it burns up to about 500 calories an hour.
6. Walking with poles: Studies show it can boost your calorie burn by more than 20 percent without making your walk feel any harder.