One thing I found very helpful in maintaining goals was a workout journal. Every day, log your workouts and whether or not you met your goal for the day.
Example: Friday 1/27: Ran 2 Miles, Abs, Felt great!
Saturday 1/28: nothing :(
Trust me, it always motivates me to hit the gym, JUST for the pure fact that I won't have to mark an 'x' on a day I was supposed to workout! If you are into running, sign up for a race that you HAVE to train for! Goal-setting is a major motivation, so what are you waiting for?