Stretches

Lately, I've been getting stabbing aches and pains in my legs and arms; given how many hours of my free time are spent in front of my pc, it's a no-brainer as to the cause. One scary article about blood clots and a Google search later, I came across this site:
http://www.tropsoft.com/ergotimer/stretch.htm

The stretches are easy to follow, requiring neither specialist equipment nor rubber joints, and they only take a few minutes. There are probably better sites out there, and by all means point me at them if you know of one.