I think the best motivation for work is salary. If you are having a big salary, it can lift your morale every month looking forward to payday! Also, don't forget to unwind every once in a while, get together with friends, hang-out with family, and don't forget to give yourself a treat.
Not all the time, because there are still some people who depends on appreciation of someone in their work as a form of their motivation. Salary may also motivate someone to work harder, but I cannot consider it as the best. And when you really felt tired, those money can't bring you up, but those someone who believes on you/appreciate all your work can. Appreciate someones work is the best way to motivate people!