My Motivation... Gas prices, Work parking fees, and traffic jams.
My commute is approx 10km each way.
I save $1200 a year by not driving the car (just in gas costs)
I also save $600 a year in parking fees minus the $100 I pay for my bike box.
Also if I drive to work I have to park 1km away from my office, the whole time I'm walking I think to myself "I wish I had my bike right now"
I found that once I commited to riding everyday I didn't need to motivate myself on a daily basis. If there is no other option it's really easy to ride, I just don't give myself the option to not ride.
The last time I drove the car to work was the begining of October, yes even through the Canadian Winter.
I am trying to ride 100% of the work days in a year. Last year I rode 96% of the days I worked.
Anytime I can Ride instead of Drive, I Ride.