Take before and after photos. I had gotten complacent about my eating habits, etc and 9 months and 45 pounds later, I posted for an "after" photo. I staged a largely mirror image shot of the before photo and put them together with Gimp.
Our spin class at the local Y had a "biggest loser" type challenge for the past 8 weeks and I came in 2nd over all percentage of body weight loss.
That was after already having lost almost 30 pounds before I started.
Of course, my bride is enjoying the benefits of the lean, less stressed Mr EE as well.
After the past couple of days of on-call activity (up 23 hours yesterday, good thing Mrs EE is in NYC with her mom) my eating choices haven't been so good. But I'm hoping the two hour fund raiser spin class yesterday proactively addressed any damage I may have done with late night at work vending machine grazing

I could post a link to the before and current.
My goal is to return to my weight when I left the Army back in 1992 AND be able to do as well if not better on the PT test.
Sorry for the long missive. I think you simply pick what motivates you, and use it. For me, it's measurable progress. Be that the amount of work I can get done, such as how long does it take to do 4 miles on the cross trainer, or what weights and reps are in my logbook, or how well I'm performing in the days boot camp workout, or the top resistance I can tolerate on the stationary bike in spin class.
Then there is dropping 2" from my waist, getting off my BP meds, low resting heart rate.
I'm a numbers guy, so seeing the numbers move in a good direction are motivating.