Other apps also existed, but they either cost money or didn't really strike me as too useful. Then came along RunKeeper Pro (iTunes link). Normally $10, right now it's free in the app store
Here's what it does:
You start up the app and select the type of activity you want to do. You can also select a playlist from your iPod to start playing (I don't - I just start up my audiobook). Then you start your activity. With the aid of GPS, it's able to track your location, distance, mile splits, elevation, total time and approximate calories burned, and more. Here's what a 3 mile run looks like:
There are also a bunch of settings. You can have the app tell you your time, distance, pace, etc. It can do it every mile, every 5 minutes or on-demand. You can also manually enter in runs for when you're on a treadmill. When you're done, you get a nice summary of your results.
Then you head over to the website. There you can see all your activities with a beautiful dashboard displaying how your run went. It's interactive too - giving you more detail as you hover over different parts of the display.
Finally, you can link to Facebook and see your friend's workouts (for example, I can see what Jessi's been running). You can also link to Foursquare and pick-up a 5K badge once you run that far.
If you run, and own an iPhone, I highly recommend picking up this app, especially since it's free for the rest of the month. I enjoy looking at the data and tracking my progress. I'm sure this will get even better as I start running longer distances. Being able to listen to audiobooks while running was huge for me, and this will make running even more enjoyable.