Touch Your Toes
It might not be the most impressive thing you see but you can't deny that a runner who can crank out the miles AND touch their toes has a certain something about them. This stretch obviously helps to keep your hamstrings nice and light which can be a common problem with runners. It can also make you faster and less injury prone!
Start in a seated position with one leg tucked in towards your waist and the other leg out to the side. Take your body and reach out towards the leg out to the side, reaching from your waist and not from your back so you are stretching the right muscles. Hold that position for about 30 seconds and then repeat on the other side.