The Maltese Falcon – George Raft was well-known for turning down roles that made Bogart’s career: High Sierra (41), Maltest Falcon (42), Casablanca (42). He refused Falcon because he didn’t want to work with first-time director John Huston! As for High Sierra, Paul Muni also turned down the part.

Lawrence of Arabia – David Lean’s first choice was Marlon Brando, who decided to make another film first, luckily for us after seeing his British officer in Mutiny on the Bountry remake.

The Man With the Golden Arm – another part turned down by Brando, this one reviving the career of Frank Sinatra in a gritty role as a heroin addict. Brando may have performed it better, but Sinatra looks more the part for this. Brando won an Oscar for On the Waterfront (best actor), while Sinatra won one for From Here to Eternity (supporting actor).
It Happened One Night – one of my favorite goddesses, the queen of cool Myrna Loy turned down the part of the runaway heiress that won Claudette Colbert an Oscar. In fact, the film was the first (until Cuckoo's Nest) to win the big four of actor, actress (Gable), director (Frank Capra) and picture. I have to believe that Myrna (The Thin Man series) would have been even better in this part, no one shows disdain of maleness quite like her.

The Graduate – Robert Redford was first offered the role of Benjamin Braddock by Oscar-winning director Mike Nichols, but he felt that he couldn’t portray the naïve college grad, which of course made star Dustin Hoffman famous. Overall, the casting was excellent, including Buck Henry in a small part as the desk clerk at the hotel where Braddock went for the affair.
Giant – Alan Ladd felt that he was too old to play Jett Rink, who was ironically aged with makeup anyway, in the multi-generational epic Giant. The role, of course, went to James Dean, who was nominated for a record two posthumous Oscars (East of Eden was the other), as all three of his films were released after his death in a car wreck. He was driving at a high speed when a car pulled out in front of him on the highway; ironically his passenger only had minor injuries.

Gone With the Wind – the role of Scarlett was first offered, understandably, to Bette Davis, who had played southern belles before with great success. Thinking she would be co-starring with Errol Flynn, she refused. Vivien Leigh, wife of Laurence Olivier, won her first Oscar in the role; her second would be in A Streetcar Named Desire.
The Wizard of Oz – the title part was actually written and tailored for W.C. Fields, who reportedly turned down the part because he wanted 100k and the most that MGM would offer was 75k. It seems like such a small amount for the connection to have been missed, and in fact, Fields’ agent actually said he really wanted to work on the script for You Can’t Cheat an Honest Man instead.
My Fair Lady – rather than come out of retirement, James Cagney refused the part offered as Alfred P. Doolittle, father of Eliza. Performing two musical numbers with style and humor (With a Little Bit of Luck, and Get Me To the Church), Stanley Holloway turned in the performance of his career and received the Oscar for supporting actor. The scene where he haggles with Rex Harrison over payment for his daughter is classic. Once again, the audience got lucky here!

Ben-Hur – the title role was first turned down by Burt Lancaster, whose athleticism and build would have been perfect for this. Instead, Charlton Heston won his only Oscar in Wyler’s record-setting 11 Oscar movie. Heston had taken a supporting part in Wyler’s The Big Country just before this, so he was due a starring role. All actors wanted to work with Wyler, whose was notorious for winning Oscars, as his films were nominated for a record 127 Oscars, winning a record 39.
The Three Faces of Eve – choosing her roles very selectively, Eva Marie Saint turned this role down (in spite of her name!), and Joanne Woodward turned in the performance of her career as a women with at least three distinct personalities, winning her only Oscar as best actress. Of course, she later married actor Paul Newman, who won his only Oscar for The Color of Money, a reward for a career of distinctive roles.