Stretching!! This is important to do in the morning before and after you wake up. And also at night. If you sit at a desk all day you can get up and stretch midday! It only takes a few minutes everyday, but after a few weeks you will notice a big difference. And it's free. http://exercise.lovetoknow.com/Free_Stretching_Exercises_Illustrated
You can use furniture to rest your legs on or a door frame for your arms when you stretch.
I have felt so much better just from stretching.