One of the main benefits of yoga is that it teaches you to listen to your body, to be in touch with the subtle cues that your body is constantly giving you. People often notice that there are imbalances in their bodies after a few yoga classes. Muscles that are supposed to be working are weak, their function overtaken by nearby muscles, which in turn become too strong. Running with these imbalances can lead to tight, brittle muscles at best and injuries at worst. Working on these imbalances through yoga can conserve energy that was being wasted on tight muscles, making your running workout feel that much easier.
Yoga is considered a precursor to seated meditation because when performing yoga postures (asanas), the yogi focuses his gaze on a fixed spot or drishti (literally "gaze"). This develops dharana, or concentration, described by Patanjali in the Yoga Sutras as "the binding of consciousness to a single spot." In the classical, eight-limbed system of yoga described by Patanjali, the last three limbs are dharana, dhyana-meditation, and samhadi-Enlightenment. By developing dharana, we can move onto dhyana. Adding a few sessions of yoga per week into your normal running routine will teach you to incorporate dharana while you run. You can do this by focusing on an outside drishti, or by making your "drishti" your breath or even your body's subtle cues.
In the following video, I lead you through a ten minute sequence that will strengthen the upper body and core and stretch out the lower body. Feel free to learn the poses first and hold them for longer than I do in the video. Do this sequence only after a proper warmup. After all, the goal here is to prevent injuries, not cause them. Do a few Sun Salulations before the workout, and lie down in Savasana for a few minutes afterward to center yourself. This particular workout is meant to be done at a different time than your run-either on alternating days or at a different part of the day than right before or after running.
Part 2 contains poses you can do at the same time as your run. Pre-run poses are Virabhadrasana I and II (see Yoga Journal's description of the poses here and here). They'll warm up the legs and develop focus. Post-run poses are Baddha Konasana (Yoga Journal describes it here) and Supine Baddha Konasana, or the goddess pose to relax the body and lengthen shortened muscles.