I recently fell in love with this "must have" and think you should have one too....the KETTLEBELL.
Along with the SandBell, this is the smallest, most dynamic piece of workout equipment one could possibly own. They come in several different sizes and most of them are in kilograms. I joined my first kettlebell class about 3 months ago. I didn't really know what to expect, but it wasn't much. The class is only 30 min and all we were using were these little bells. How hard can it really be? Holy cow was I wrong. It kicked my a**. I was sore for a week, not even exaggerating. I recently started using the kettlebell with my clients. Let's just say they HATE it, that's because it gets the job done. It adds so much more intensity to their workouts.
Here is a great kettlebell video courtesy of Crossfit Central.
Now go out and swing some bells!