There is nothing quite like running. Cheap, effective, and always available to you wherever you are. Got shoes? You can run. So when I found Podrunner for my iPod, I was elated.
What is it? They are a series of running music mixes based on beats per minute (bpm). You can equate a beat with every foot strike. The faster the bpm, the faster your running pace. Every single one is different. I like them because they set my pace and keep me focused. I always run solo, so this is a huge help to get in a great workout on my own. Even better......they are free. Yes, you heard me. They are in iTunes as podcasts (FREE!) and there is also an app for the iPhone (FREE!)
If you are training for a long road run or marathon, you might also want to check out Podrunnner: Intervals. Don't know anyone who likes intervals, but they are a necessary evil if you are trying to build speed and endurance. (One of the reasons I hung up my racing flats and settled into long, easy runs!)