Stephen King

To truly answer this question would take more time than anyone should bother with, but I can give the overall differences:

• Missing from the movie was the character of Patrick Hockstetter, as well as a few more minor characters, and the history of the monster in the town of Derry. In the movie, Beverly didn't have sex with the boys in the tunnels on their way out after they believed they killed the monster when they were 12 (early).
• The character of Beverly Marsh in the book was a very tough tomboyish girl who didn't take crap from anyone (except her father). In the movie, she was played by actresses who portrayed her as very meek, both in her 12 year old and adult years.
• The movie left out the entire part of the book when they were in the "macrospace" and mentally fighting the monster. In the movie this was simply portrayed as them being hypnotized by the monster.
• In the movie, the 12 year old group never made it to the "lair of it". They met up with Pennywise in the cellars in some random place.
• No mention of the Turtle in the movie.
• Many interactions with Henry were left out of the movie.

There are so many more differences, but I think I hit on most of the ones that really took away important context from the movie version.

She is borderline psychotic (progressing steadily into full-on psychosis as the novel/movie progresses). Even just 1/4 of the way through, the writer character (Paul Sheldon) has already voiced his concern (to the reader, of course) that Annie Wilkes is borderline psychotic:

"Because of his researches for Misery, he had rather more than a layman's understanding of neurosis and psychosis, and he knew that although a borderline psychotic might have alternating periods of deep depression and almost aggressive cheerfulness and hilarity, the puffed and infected ego underlay all, positive that all eyes were upon him or her, positive that he or she was starring in a great drama; the outcome was a thing for which untold millions waited with held breath.

Such an ego simply forbade certain lines of thought. These lines were predictable because they all stretched in the same direction: from the unstable person to objects, situations, or other persons outside of the subject's field of control (or fantasy: to the neurotic there might be some difference but to the psychotic they were one and the same).

Annie Wilkes had wanted Fast Cars destroyed, and so, to her, there had only been the one copy," (Viking Penguin hardcover edition, p50).

The Rose Red mansion does not exist. It was purported to be a true story, but it was a hoax, just like with The Blair Witch Project, The Texas Chainsaw Massacre, and others. However, Stephen King got the idea from Sarah Winchester and the Winchester Mansion, which did/do exist. See the Related Question below.

It is not a real place but you could find fake pictures of it, and pictures from the movie, on Google images.