In reply to Dom Whillans:
Depending on what tickles your fancy, there is a good book called yoga for athletes (written by triathlete who is also a yoga teacher), which has post run stretches to do. Ooooooh pigeon pose is tough on the arse. I like the book a lot, but its probably best if you have a basic idea of yoga poses to start with.
And +1 to the foam roller suggestion. Spiky massage balls are also good for getting at knotty calves. If its not agonising you are doing it wrong