Here's an argument that utilitarianism -- the theory that the moral worth of an act comes from the ratio of pleasure-to-pain that it causes -- is false. http://www.stumbleupon.com/stumbler/Algebraic0/review/44513351/ (Yeah, it's presumptuous to link to your own review, I just don't want to waste space writing the whole thing again)
Once you accept that the material consequences of an act are insufficient to determine its moral weight, it is a small step to Kant's declaration that "the only thing that can be called good without qualification is a good will". That is, while material consequences are always morally ambiguous and often unforeseeable, a person's moral intent is fixed and unambiguous. A system of morality, therefore, must be anchored in the will and intent of a free, rational being rather than in physical circumstance. So if we want to find out what the right action is, we have to ignore the specific material situation and instead focus on deriving a moral law -- a categorical or universal imperative -- that holds for all free, rational beings. Such a law would (according to Kant) dictate that each being does only what it would be possible for all beings to do. So "there is only one categorical imperative, and it is this: Act only according to that maxim whereby you can at the same time will that it should become a universal law."