I have fall in love with Strava - minimal iOS running app (http://app.strava.com/mobile). I am not affiliated with them in any way.

I can also second Hal Higdon's site above.

A lot of people in a recent half marathon I ran were using the half marathon as a staging ground for their full marathon. By running a half marathon/5k/10k you can get a feel for what running an actual race feels like, which is invaluable.