Can you suggest any exercises to do while sitting at work?

I can sympathize with this situation. There are days when I'll be stuck at my desk for hours at a time. Having dealt with this for some time now, I have developed effective strategies for keeping my body moving. Every hour I try to do a few back exercises and neck stretches to counter balance the sitting. For the back, I squeeze my shoulder blades together and hold the position for about ten seconds and repeat this three times (this exercise is shown on pages 212-213 of Strong Women, Strong Bones). For the neck, I relax and place my right hand on the back of my chair seat and my left hand on the top of my head. I then gently pull my head down to the left side, really focusing on my lower neck, shoulders and upper back. I hold the stretch on one side for about twenty to thirty seconds and then repeat on the other side. When I am on the phone, I stretch out my toes by lifting my legs out straight and pointing my toes up and down as far as they will go. And finally, I try to get up out of my seat as often as I can.