A Vote for the Remnant
Roderick Long and Keith Halderman have summarized some of the reasons for voting Libertarian but let me give the one I prefer to emphasize. In my view, it is important to keep the Libertarian party alive to fight again in four years. In a small way, my vote can help do this. Perhaps next time, the LP will try to recruit a better known candidate such as Penn Jillette (now that would have been wonderful!), Drew Carey, or Kurt Russell. Unfortunately, it didn't do this so I will cast my vote for the keeping alive the remnant. The term remnant was first used in a similar context by the great libertarian Albert Jay Nock.
Somehow it is appropriate that today is the birthday of William Graham Sumner (mentioned below by Roderick). He too faced an impossible election choice in 1900 between two candidates he abhored. As in 2004, the question of imperialism was a central issue in the campaign. In the end, Sumner voted for an uncommitted slate of electors who represented the nearly defunct classical liberal National Party rather than voting for McKinley or Bryan.