What are you worth? What is your value?

In my last blog I asked a question like: What is it about me that I can change and become a better me for 2010?
How about taking a look at your value. What are you worth? One of the greatest difficulties I see is that people have a hard time valuing themselves highly. For example when a person takes a job it is usually based on a need and not what they are worth? The business person decides upon a value for their service. What do they value their services for? It seems like a struggle for them to determine what should be charged.
WHy do people and perhaps you, struggle so much with how much they or you are worth? Why do people under value themselves? What keeps people from highly valuing themselves? WHat do you think? I would be interested in your opinion.