Stability ball, swiss ball, therapy ball, whatever you want to call it. If you don't have one, run out and get one now! This is one handy fitness tool to have at home and at work.
You can do a variety of exercises for every single muscle group with one of these. By incorporating a ball into your routine, you will work multiple muscle groups at once, maximizing your caloric burn. You also constantly work our core stabilizing muscles, making for a more stable back and joints and stronger abs.
You can use a ball at the office, provided you have a health conscious boss. As a society, we are sitting in front of computers and TV's for longer periods of time. If you work in an office, you're most likely sitting in front of a computer all day long, causing you muscular imbalances and back pain. If you use a ball as an office chair it will help prevent low back pain and you can get an ab workout in while you get your work done. Two birds with one stone. Sounds great to me!
You can find a ball pretty much anywhere. There are a few things you want to look for though. First, make sure you get a burst resistant ball. These balls have a tacky kind of texture to them. This is really important for those who have kids. The last thing you want to to do an exercise and have the ball explode from under you. The burst resistant balls will slowly deflate if punctured, saving you and your family from injury.
Secondly, get a ball that's fitted to your height. Balls come in different sizes. Look on the sizing chart to make sure it will work out for you. Most women need a 55 cm ball, while most men need a 65 cm ball. This is a generalization, however.
Once you get a safe ball that fits you and your program, you'll be ready to rock!