Intrinsic motivators are said to be the most powerful driving forces behind any human action. Intrinsic being those motivations within us that have no tangible or physical form. In the workplace, and over the course of an entire career, a worker will tell you that he/she is more motivated over the long run by how well they enjoy what they do. Sometimes you will hear the response "I feel like I am a part of something here", meaning there is work being done the employee feels is important and that they are contributing to. If salary incentives were all that motivated employees, then no one would be a social worker or a public defender. No one would be a painter or an actor.
Of course, you can also motivate someone by creating a fun and friendly work environment, with good people, flexible hours, generous leave and medical or retirement benefits, and job security. The less worried a person is about losing their job or about meeting the obligations to provide at home, the happier and more productive they will be in the workplace.