I can't help but feel my motivation is somewhat different to a lot of people here, or at least the way they are describing their motivation. A lot of people are mentioning money and sex, and while they are obviously a form of motivation I see them more as short-term goals than long term motivation.
Personally, I think my motivation is simple, once I'm gone, I want to have created a legacy that will live on without me. Money and sex are fantastic, but when you're coming to the end of your life it would be good to look back and remember the great times you had with people and to know that you've inspired others than to know you've got $1,000,000 in the bank and you've slept with 40 supermodels.
Don't misunderstand me, money is important (and will help in achieving my long term goal) and sex is fantastic - but when it comes to long-term motivation they're mostly irrelevant to me.