As I train for a half marathon, I have learned a couple of things.
If you have not trained with an Ipod, I recommend you try it, not only does it take your mind of the thought "why am I doing this?" but it also helps you zone out and get into a "step" rhythm. Try and pick songs that go with your stride. Such as -stepping to the beat of the song.
To help with music choices, log on to http://www.runnersworld.com/cda/special/0,7889,s6-240-466-0-0,00.html. They have many playlists used by the pros!!!
Another thing I learned- When you are picking a route to run, focus on running somewhere where it is fun. "Sight seeing" if you will. Running through country setting will get boring over time, but keeping your eyes on different things will keep your mind of the thought " why am I doing this?"
A great site I use is http://www.mapmyrun.com/ You can drop and drag a route to decided how far you want to run, and where you can go locally though your town.