Dennis Crowley has some nice ideas for what to do with a GPS- and internet-enabled device with running software on it (e.g. Nike+ on an iPhone).
#3. Ghost racers. Think: Super Mario Kart time-trials, except you're running against a ghost version of your best time on the map. I know the Garmin already does this, but make it social... show me the best times of my friends or other local users.
