To add to Poohbear's list, there is also 'The Man in the Brown Suit' and also (as I said before) 'And Then There Was None'. This has been filmed several times under different names.
It takes place on an island with ONLY 10 people on it. There is a nursery rhyme (the contents have changed slightly to fit in with the books title changes), suggesting how 10 people will be killed. It's challenging. I enjoyed it.
