Cluedo Liars Edition Board Game - £12.49 sold by FST Groups @ Amazon

Available slightly cheaper from other sellers on Amazon, but not many reviews. Amazon selling it themselves it's £14.85, from a RRP of £26.99, and £23.20 at The Entertainer.

I like the classic game myself, but a lot of people swear by the Liar's Edition as adding an extra dimension to the game.