i have to admit i don't think much of what motivates me to run but on some occasions the thought "just fucking do it" comes to mind. nike, but with gusto :)
See mine is "Whatever you do, don't dream it, do it." Of course, when I was running my mini the other day it was more like "get the ---k out of my way."
"I may be beaten, but I will not be out-trained." What this means to me is that I know that there may be other runners out there who are faster than I am and have more natural speed but I will train to the best of my ability and strive to maximize my own potential. When I win a race it is because I have trained harder and smarter than others. This motivates me to prepare myself for races and reminds me that each day I don't train is a day that I am ceding to my competition.
I run to punch fast runners in the back of the head.
Anyone can catch up to a slow jogger. I want to be passing runners like Ryan Hall, Gebrasalesi, Bekele...ect. At that point I'll probably be too busy setting world records to worry about punching them. This is the time where my alarm clock goes off and I wake up from my dream, but you get the point.