Kettlebells basically are hunks of iron with handles. Not very high-tech or cool-looking, but they have become popular in recent years. If you haven't tried kettlebells yet, this might be one of the most efficient ways to get a full-body workout with just one piece of equipment.
In one 20- or 30-minute routine, you get the benefit of strength training and an aerobic, fat-burning workout. You even can crank up the music and take it outside for a change of scenery.
For beginners, start with 5-, 10- or 15-pound kettlebells, available at local sports-equipment stores and most gyms. Start with two sets of 10 repetitions for each exercise. As you get stronger and more comfortable with kettlebells, work up to three sets of 10 or more.