There are quite a few "run tracker" apps in the App Store (I know our own Erica Sadun is a big fan of RunKeeper). However, RunMonster is also worth a look, if only because it's just plain gorgeous. It lets you do all of the usual things: track your runs and bike rides, keep stats on your workouts, or see maps of where you've been according to the iPhone's GPS. It goes further than that, though, with a very elegant and charming interface, and surprising ease-of-use. It will automatically name your runs according to streets, and it'll even group your runs and figure out whether you walked, biked, or ran, according to your speed.
Even if you've already picked a running helper, give RunMonster a consideration. There's a free version to try out, and a US $9.99 version fills out the feature list nicely (with sugar like music controls and gestures) if you like the app. Like most of the great running apps out there, it won't necessarily make you a better runner, but it probably will make you enjoy the journey more.