There is no evidence that static stretching immediately prior to running has an effect on injury prevention. There is also some evidence that static stretching before running can cause decreased strength and negatively affect performance.
Therefore, you do not want to static stretch before you run. The best way to warm up and stretch your muscles is through dynamic stretching. I will describe a few of these "stretches", but this link and article at Runner's World is awesome and I highly suggest you take a look at it
With all dynamic stretch movements you want to land on the ball or mid-sole of your foot. Also, keep your foot dorsi-flexed (this means don't point your toe...like a dancer would, keep it flat)
High knees: In a standing position lift your leg straight in front of you. You want your knee to make a right angle and your thigh to be parallel to the ground. Look at this position in a mirror or reflective surface so you can get it in your mind. Now do this motion quickly with each leg as you move forward. It helps to put your hands out and have your knees touch your hands so you know you are getting them high enough. Remember, do NOT land on your heels.
Frankenstein: Keeping your back and knees straight, walk forward lifting your legs straight out in front of you. Its kind of like a toe touch, with your leg in front of you instead of to the side. This is great for your hamstrings.
Carioca: I don't exactly know how to explain this one except you might know it as grapevine.
I really like this video to show you all the different exercises. Except that in the very first exercise, high knees, the guy is landing on his heels! Ah!!! Rookie mistake, please don't do it!!!
This video is also pretty good. You can start it around :40 and you can disregard step 5 at the very end of the sport specific part. The drills described here are a little different than the ones I generally do but they are really good as well.
So there is some dynamic stretching for you. I don't do this before every run, but it is good to. I usually do it on days where I am going to be doing a tempo run or a speed workout.
So on to static stretching. Don't think that static stretching is bad for you; quite the contrary. Static stretching is great for you. Just don't do it before a run. But DEFINITELY do it after EVERY run. Hold each stretch for 15-30 seconds. This will keep you from cramping, being as sore the next day and help prevent injuries. You can do any stretches you want, but here are a few that I highly suggest you always do.
IT Band stretch: This may be the most important stretch you will do. IT band syndrome sucks bad and can keep you from running. If you remember to stretch it after every run you will hopefully avoid getting this injury. There are a bunch of different ways to do it, but this one is the one I personally like best. The leg that you aren't grabbing doesn't have to be bent, it can be straight, or you can bend it up and use it to support your other leg.
Hamstring stretch: My hamstrings are always tight. And did you know, tight hamstrings can cause lower back pain? As with every stretch, there are different ways to do it. This picture is just one example.
Quadriceps stretch: I like this picture because it shows the guy grabbing his opposite leg. Grabbing your right leg with your left hand and vice versa prevents putting extra strain on your knee which could cause injury.
Calf stretch: My calves also get really tight and if you are incorporating a mid-foot strike (like you should) then your calves will definitely need this stretch.
It is not necessarily important to be flexible as a runner, but it is definitely important to stretch your muscles, both before and after you run. Hopefully now you can do it safely and effectively!
Questions? Comments? Why do/don't you stretch?