Gaz,
You should be looking to stetch the follwong muscle stretches:
Quads, calves, hamstrings, hips, glutes and possibly your lower back. Some people tense up around the kneck and shoulders when they run and if that applies to you you may need to stretch out these areas as well. Try and hold your stretches for between 15-30 seconds and don't bounce.
Having a bath after a hard session can also help ease out those sore muscles. Some peeps reckon a cold bath is best but I've never been brave enough to try it myself. I also treat my self to a sports massage once a month.