Me too, and the more I run the worse it gets!
Will try some of your suggestions, the squat stretch sounds pretty good. It's been suggested to me by a few people who know what they are doing, now I just need to get religious about doing it regularly.
Just make it part of your squat warmups. I have a ritual of squat stretching, doing 20 reps as deep as humanly possible with only the bar, then doing my leg swings, and finally starting my warm up sets. It really gets me loose and I totally feel the difference it makes every day. Plus it's a nice little ritual to get me into my workout frame of mind, because I always start with squats.