My biggest motivation when running is the music I'm listening to. I like really fast, upbeat music so that it motivates me to go faster. Oh and classic rock like queen, the doors, ac/dc help me get motivated =)
"In running, it doesn't matter whether you come in first, in the middle of the pack, or last. You can say, 'I have finished.' There is a lot of satisfaction in that."
-Fred Lebow, New York City Marathon co-founder