It seems to me that we have seen people in this thread advocate two value logics, three value logics, and four value logics. You can have workable systems of logic with and without the law of the excluded middle, and with and without a law of contradiction. There are intuitionistic logics, relevance logics, classically consistent and paraconsistent logics. To say nothing of linear logic, modal logics, and ludics.
Follow the links to the SEP articles on dialethi and paraconsistency. And then follow the citations from there to learn that logic is pretty big and flexible field.
Graham Priest discusses The Liar's Paradox for a NY Times blog. It seems that one way of solving the Liar's Paradox is defining dialethei, a true contradiction. Less Wrong, can you do what modern philosophers have failed to do and solve or successfully dissolve the Liar's Paradox? This doesn't seem nearly as hard as solving free will.
This post is a practice problem for what may become a sequence on unsolved problems in philosophy.