What keeps you motivated to work out?

Find a type of exercise you enjoy (or relatively enjoy) ...and it can even be a type of workout inside a type of exercise (i.e...interval runs, Tabata, etc...)
Set a goal (I have to have something I'm striving for or I get bored out of my mind)
Set a time to exercise (like an appointment)
Recruit a friend, who REALLY likes working out, to join you
Find inspiration (this site, posters/pictures of what you want to look like, watch workout documentaries)
Listen to music while working out
Stick with it long enough that it becomes necessary (...until your body craves the exercise)
Give yourself a break (take days off when you need it) Personally, I never work more than 4 days in a row and never take more than 2 days off consecutively...usually just one day off.