From Lifehacker: BPM Analyzer Calculator!
Click the pic to take you to the Lifehacker blog to download!
I think this will be a useful tool. I'm noticing that I'm running faster when I don't have my iPod. I think I tend to run with the beat of the music, so if the music slows down, so do I. I am also certain that part of them stems from the fact that I am not yet a very accomplished runner. I do great to break a 12 minute/mile pace right now! It's all good though.
If you download it and try it, let me know what you thought of it!