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!
So, you say appreciation for some one's work is enough, huh? But appreciation without proper compensation isn't enough either, will you still be motivated if all you can get from work is appreciations? How can you support all your needs in life? Maybe, if you are rich enough and work is just a kind of past time or hobby for you. That I can consider appreciation is the best. Nonetheless, meh.
BTW, what is your reason why you work in the first place? As for me, is to earn money so that I can support all my needs and be stable on my own until to save enough to start my own business in the future. ;-)