Here is an excellent article on yoga and running I found over at Daily Cup of Yoga blog.
This article has a complete sequence of yoga poses specifically for runners along with pictures (always helpful) With running yoga is especially helpful as it helps to prevent injury, increase stride length, and loosen the pesky IT band that tends to be particularly troublesome for athletes!
Yoga is the perfect compliment to running as it loosens the hips, hamstrings and lower back muscles which will improve your posture while you run. Improved posture also means improved breathing, which of course means better athletic performance! Yoga is to Running as Yin is to Yang