What movie has come the closest to it's source material?

Attack of the killer tomato... Maybe  ? I don't understand your question zack :( and I don't know if that's a real movie ... I think it is though.

Apollo 13 was pretty close. I saw a show the other day about just that. They added some flair to actual events, but they didn't add events. For example the most famous line of the movie, "Houston, we have a problem." wasn't the actual words said. What was actually said was, "We have a problem, Houston." It isn't as dramatic.

War of the worlds

America: Freedom to Fascism

"The Last Star Fighter" . . .

Was weird to watch the movie after having read the book . . There was literally no room left for anything out side the story in the book . . . I could almost recite the damn lines.

I will give you three that I found quite accurate...

First, SHAKE HANDS WITH THE DEVIL, the story of Canadian General Romeo Dallaire and his utter agony during the Rwandan genocide... Dallaire could have prevented that if the UN had supported him adequately. Back home, he attempted suicide several times he was so haunted...I did watch the movie but was unable to complete the book, so horrific.

This winter I saw the 1964 movie LILITH, a fine rendering of the book by J.R. Salamanca. Jean Seberg and Peter Fonda were superb...and Warren Beatty was fine also. But I did not know how well the movie was done until reading the book, such a movie cannot, could not stand on its own, I felt; its exquisite, sympathetic, sensitive portrayal of madness.

Last, the 1951 movie THE AFRICAN QUEEN; if anything it was better than the 1935 novel and that is not to take anything away from C.S. Forester - it's just one of the greatest movies of all time.

Aside from the non-story-line ramblings, The Princess Bride followed the book closely.

Also the novel(which I truly believed was the screen-play with all the stage directions omitted) for Star Wars III - the first movie-followed the story exactly and was so terrible that had I read it before seeing the movie you couldn't have gotten me into the theatre with a team of horses.