I will explain this and hopefully get a mod to sticky this post.
First, you are making a mistake by stretching *before* running. Stretching causes many more injuries than it prevents - mostly because people stretch *cold*. Before you start your stretches, you need to warm up your muscles, limber them somewhat, by running maybe a half mile or so at a very easy pace.
You can also do a stretch after your workout.
I've seen a lot of studies on stretching - some show no benefit, marginal benefit, or a detriment. I doubt the science behind a lot of them. My final conclusion is that you only really need to stretch when you are moving your muscles out of a normal position, and often the exercise you do (especially in lifting) *is* a stretch and doesn't need any extra stretch.
The most reliable study I saw on stretching backs this theory - it had just one subject, Michael Johnson - about the fastest man on earth. By stretching, he gained a fractional amount of time on the curve of the track (meters 0-100, 200-300). Why? Because the motion you use when running that fast on the curve is slightly beyond your normal range of motion when walking/running.
Why do I stretch? Because it just feels slightly better. And that's reason enough for me. I usually warm up about a mile, stretch, and finish my warmup with another mile or so.
What stretches do I do? Hard to illustrate on the board. They take about 5 minutes total. Here is a website that explains some of them:
http://k2.kirtland.cc.mi.us/~balbachl/stretch.htm#Calves
Also, see what it says at the very top: "NOTE: Before performing any stretching exercises, make sure you warm up for 5-10 minutes!"