While you're pushing through your workout on the treadmill, elliptical, or whatever it may be, imagine yourself doing something you've always wanted to do or learn how to do.. and SUCCEEDING. This pushes me to want to workout even harder because I know the more I push myself now, the more I'd be able to push myself to finally do what I've always wanted to do.
I imagine myself breakdancing as my workout in my gym's bball court with a little bit of an audience. I've ALWAYS wanted to learn how to breakdance, but never felt like I was in good enough shape to even try. Imagining myself actually doing it makes me want to work that much harder.