You may already know all of this, but I just wanted to cover the bases. I see so many people doing things wrong, well, not WRONG, but not in the best way, so let's clear things up.
DO NOT stretch before your workout. WHAT? A rather new idea, but study after study, article after article, journal entry after journal entry has confirmed that stretching pre-workout is inefficient and potentially damaging. 1. you are stretching muscles that have not been warmed up yet and are therefore not elastic, which can actually lead to injury. 2. stretching pre-run/workout/walk/whatever can actually weaken your muscles for the next 10-15 minutes (and who wants that when they're trying to bust out some 200's?). DO WARMUP. This means start with a nice easy jog or walk of 5-10 minutes before you try to break a world record.
DO stretch after your workout. Stretching your now warm and elastic muscles will really benefit you most for you NEXT workout. You are gaining flexibility/balance/strength that will help you be more relaxed and keep injuries at bay.
DO YOGA. If you are still doing the hurdle stretch and the old arm pull across the chest, you really should stop. Please do yoga. The benefits are overwhelming. Flexibility/balance/strength/focus are all part of yoga. You'll gain more from 5 minutes of yoga then 10 minutes of your 1950's toe touches. It's easy to browse a yoga index (provided by yoga journal and linked at left), check out some books from the library, or buy a few yoga videos (think Rodney Yee).
*extra bonus tip* runners who tone and improve core strength run up to 33% better (that can translate into big minutes!)