I have a folder of motivational pictures, some of before/afters and others of women with body ideals of mine.
I also keep motivated by buying little treats, like a nice body scrub or a nice top, etc.
When I don't feel motivated, I still stick to my plan, and more importantly, my exercise.
Exercising motivates me the most because even if I feel like not going, I go and after that I'm like, yay I went and did it, now I can feel proud of myself.