You didn't actually comment on whether polygraphs actually work, or at least how successful they are. Surely you can cite a decent study on false positive and negative results - I'd be particularly interested on how training can increase the odds of avoiding a "liar, liar, pants on fire" result. Also if being a sociopath or psychopath helps you pass a polygraph.
Reading microexpressions is another technic some people swear works - there's a whole TV series about it "Lie to me".
Finally, if you are fascinated by the possible impact of an infallible lie detector on society you'll love reading the book "The Truth Machine" by James L. Halperin. That's the author's website and there's even a download link for a Word doc of the book. With a little help from Google I was able to convert it to macro-virus safe, non-Microsoft friendly PDF you can download here. If you enjoy that his book on immortality is also a very interesting exploration of the subject IMO.