If you know me, you know that I spend a lot of time telling people that you don't need fancy equipment to get into great shape and stay that way. In fact, that's much of the reasoning behind the whole FitDaily site. But, I still do like playing with all the latest fitness toys.So today I want to discuss one of my new favorite pieces of equipment that I've been using. It is a bit pricey, but it really is a lot of fun. It's called the BOSU ball, or BOSU Balance Trainer. BOSU means "Both Sides Utilized."
Basically it's half a ball. So it's got a flat side and a curved side. The whole point is to unbalance you. Squats on the bosu ball are probably my favorite thing. I do some air squats and then move up to back squats (with very light weight) and finally to overhead squats.
It's also a neat way to do other exercises, while staying balanced on the ball. This is a case where weights (dumbbells especially) come in handy, because you can't do a whole lot with resistance bands while using the ball.
What's most interesting is that both sides feel fairly different. If you put the the round side down and stand on the flat part, the whole thing wobbles. But, since it's an inflated ball you can actually bounce a little bit to keep your balance. If you flip it over and stand on the half-ball with the flat side down you get the opposite feeling. Bouncing one foot actually tends to push your other foot off the ball, causing you to lose your balance.
There's other uses too, such as laying over it to get more range of motion on your situps, or to do push-ups on. If you're really brave you can try balancing on one leg.
Anyway, it is a bit pricey. The best deals I've found are around $99. I've included some links for those interested.
Here is a photo of the contraption: 
BOSU ® Ball Home Balance Trainer - Discovery Channel Store
Fitness Quest Bosu Trainer – Buy.com
Overall it's a fun piece of equipment. It's certainly not a requirement to get in shape, but it is something to have fun with and definitely great for building your balance.