I don't believe in free will. A neuroscientist in the 80s (Benjamin Libet) did an experiment where he measured brain activity while people made 'free' choices. I don't remember all the details, but it was some simple task like pressing one of two buttons. Then he asked them to estimate when they'd made the choice. Anyways, the basic finding was that the frontal cortex had an increase in activity shortly before the subjects felt they had made their decision.

The interpretation was that the activity in the brain was making the choice and the subjects only became conscious of it later, and their subjective impression of having made the choice themselves (rather than their brain chemistry having made it) was itself only a by-product of brain activity.

Further, people who suffer damage to the frontal lobes often suffer adverse effects to motivation and will in a manner suggesting that these things exist in the frontal lobes. For example, a person who loses part of their frontal lobe may become unable to control their impulses, doing crazy things like fondling women's breasts in public or losing their temper for no reason (like Phineas Gage, the guy who got an iron bar shot through his brain). Others may develop an inability to inhibit actions such that whatever object is set in front of them, they will automatically grasp it and start using it ("Alien hand syndrome"). These kinds of phenomena suggest to me that 'will' is a function of brain tissue and thus as far outside of our conscious control as the function of the heart or liver.

In fact, to most neuroscientists this whole debate is a bit silly because they believe that all thoughts and behaviours are the outcome of activity in the brain, and that we do not have a little man in our head who is 'me' pulling levers or whatever.