I use an app on my phone called Fitocracy (Fitocracy on iTunes / Fitocracy on Android ) to keep track of my workouts. It's not the best tool for this function but it does have on interesting feature that I love. They use the concept of points to rank your workout. After you achieve a certain number of points you "level up".
If you have ever played a video games with levels then you know just how addictive it can be to "level up". I played EverQuest (You know, before World of Warcraft even existed!) for years, and the time trap you would find yourself in was just trying to get to the next level, or to get the next piece of gear.
So why does this help with your workout? Let me give you an example. I was exhausted this morning. The day hadn't started right, I didn't have headphones, and it took me longer to get to the gym than expected. I plowed through a pretty decent workout, but I was going to skip my after weights run. So i entered what I'd done into Fitocracy, and lo and behold I'm 94 points short of a level.
I looked at it for a second and said well fuck, I guess I'll get that tomorrow. I walked ten feet, and said to myself damn it! Its 94 points! I can get that with one more hard set of exercise. So I turned my ass around and worked a little bit more. It was a little trick, but it caused me to push myself just a little further and get me closer to my goal just when I needed the inspiration the most. If I'd worked myself hard enough I would have been satisfied, but I hadn't, so I wasn't and that little 94 point reminder gave me the push I needed today.