Here are a few book rejections I bet editors would like to take back...
Carrie by Stephen King -- "We're not interested in science fiction that deals with negative utopias. They do not sell." Lust for Life by Irving Stone - "A long dull novel about an artist." (After sixteen rejections, Stone found a publisher and the novel sold twenty-five million copies.)
The Diary of Anne Frank - "The girl doesn't, it seems to me, have a special perception or feeling which would lift that book above the 'curiosity' level."
Gentlemen Prefer Blondes by Anita Loos - "Do you realize, young lady, that you're the first American writer to poke fun at sex?"
Crash by J.G. Ballard - "The author of this book is beyond psychiatric help."