As backwards as it is, my best motivation comes from running a race without training. I know this is how people get injured and burnt out, but it also allows for me to get out there and just run. When I hop back into one of these races without training, I have no expectations. My only goal is go and run. From that I also can figure out what my current average pace is and determine a realistic goal for my next real race. Last fall (09) I did exactly that, I ran the AFC half marathon in at 2:27:02 with an average amount of running. I ran a few days a week, but without any intervals or speed work. I began following a training plan and raced in the SilverStrand half marathon and improved my PR to 2:13:06. Since that race I have plateaued around that pace, with a new half PR of 2:09:36.
It's been about 7 months since my last race and I've been having a hard time getting motivated. I am however signed up for a 10k this upcoming saturday. I've been running some, around 4-5 miles so I feel confident that I will complete the race, but it will still be more of a motivation run to know what my current pace is in order to start training for the spring season of races.
I also have some added motivation/compeition coming up, my high school friends and I are running a half marathon in September and I definitely don't want to be the last once coming in through the chute.