I find, for me, that a week is a good chunk of time for motivation. I use a planner and at the beginning of the week, I write down when I am going to exercise and what I am going to do. I also write down my food goals as well. As the week progresses, I circle the workouts I did with time and or distance (if its running or biking) next to it. Sometimes I write down the calories for each day as well.
Fitday actually does this a little in the calendar.
At the end of the week, before the next one, I review what I did and how close I came to my goals. I also try to think about how I can do better the following week or what changes I need to make. Then I set up my goals for the next week. Sometimes I have good weeks and sometimes bad, but I never give up completely and its usually not too hard to get back on track.
I hope this helps or gives you some ideas.