"Misery" is probably one of the best films based on a Stephen King book, and what about "The Shawshank Redemption" and "The Green Mile", also both based on Stephen King stories/novels...
I would have to say that the worst film I have seen is Matrix Revolutions (I did actually get up and walk out half way through).
Another really bad film has to be almost everything with Tom Cruise in (Eyes Wide Shut, MI3, Vanilla Sky) and of course Bewitched (that was awful.