It ought to be mentioned that the end is not, as many people have mistakenly assumed, the acquisition and maintenance of power by a ruthless and control-hungry tyrant. Rather, Machiavelli thinks the prince ought to do whatever is necessary for the preservation and the benefit of the state. This becomes clear in the contrast he sets up between Agathocles of Syracuse and Cesar Borgia: the former is just a power-hungry thug whose only concern is his own power. Borgia, on the other hand, is an exemplar of a ruler who displays Machiavelli's version of virtù because he manages to simultaneously "satisfy and stupefy" his subjects through a single act that makes them both revere and fear him.
Anyway, why listen to me when we have the always brilliant Quentin Skinner lay down some historical and philosophical wisdom in the following interview with Nigel Warburton:
And if you can't get enough of Quentin Skinner, you might want to check out a fascinating lecture he delivered a couple of years ago in Cambridge on "What Is Freedom?"