Diamonds Are Forever: the book was about diamond smuggling, the movie about a diamond-driven laser or similar gubbins.
Moonraker: the book was about a missile of that name which was built by a Nazi who had disguised himself as a British soldier at the end of WW2. While he was supposed to be simply testing a missile, the villain (Drax) had fitted it with a nuclear warhead and was going to send it to London. The movie was about a shuttlecraft of that name. When the book was released in the US, it was under the title Too Hot To Handle. Not many people know that.
You Only Live Twice: the title comes from Bond's attempt at a haiku, as someone wrote it above.
Octopussy: the short story was about Bond being assigned to apprehend a hero of the Second World War implicated in a murder involving a cache of Nazi gold. Bond appears briefly in this story, which is told mostly in flashback and from the point of view of Major Dexter Smythe. He tries to befriend a poisonous octopus which prevents Bond from arresting him, the hardway. The movie had a completely different story and introduced a female protagonist as Octopussy who is said to be the major's daughter.