Dan Pink explores the value of intrinsic motivation at TED:
In it he compares a boss's motivation in the workplace to a mother's expectations after a Thanksgiving meal. Basically saying that putting any sort of dollar amount on that dinner would cheapen its value. In the same fashion, employees are better motivated with intrinsic manners over monetary ones. I think this is an excellent point, and that most successful business relationships extend beyond their dollar amount.
(thanks Nathan Adkisson)