A big motivation for me is to imagine putting on all the weight I managed to lose/lose the tone (ish) you managed to get after all that work. Another is thinking of the complements you get and how much better you look and feel now than before. For me comparing photos of myself now to past photos really encourages me!
If you put back on, lets say, 3lbs, dont think "oh well **** it" and continue the bad pattern - use it to gain motivation! Also remember, its not all about actual weight, think of the inches, health impact etc.
The best thing to do is make exercise a habitual behaviour - set yourself a weekly goal - for me its 3 x week for 1 hour or a little more - this could be 2 classes a week for you to start. If you dont manage it one week - make up for it the week after! And remember "weight loss" is 70% diet / 30% exercise.
Good luck
