Here, via (sort of) Instapundit, is a useful quote from Robert Heinlein:

If you are part of a society that votes, then do so. There may be no candidates and no measures you want to vote for … but there are certain to be ones you want to vote against. In case of doubt, vote against. By this rule you will rarely go wrong.

That’s not a bad rule, and, in my view (FWIW), an excellent reason to vote for John McCain