iPhone: RunKeeper is one of the most popular running apps on the iPhone, and today it gets a new goal-tracking feature called Goal Coach that helps keep you motivated. It's a slick system that works surprisingly well.
First, you pick a goal you want to achieve. This might be training, weight loss, a challenge or a race. Then, RunKeeper builds a custom plan for you based on your previous activity.
If you don't already have the iOS app, check it out at the link below.
RunKeeper (free) [iTunes App Store]