[Thorpe]

A few of my favorites;

Daniel Day-Lewis
Fellowship of the Ring
Daniel Day-Lewis was repeatedly offered the role of Aragorn.

Mel Gibson
Gladiator
Mel Gibson was offered, but turned down the lead role.

David Bowie
Batman
Bowie was considered for the role of Joker.

David Boreanaz
Batman Begins
David Boreanaz turned down the part of Batman

John Cusack
Batman Begins
John Cusack was offered the role of Batman.

Sean Connery
The Matrix
Sean Connery was originally offered the role of Morpheus. He turned down the role saying he couldn't understand the script. Years later, he said that he chose to do "the League of Extraordinary Gentleman" (despite not understanding the project) because he regretted turning both "the Matrix" and "Lord of the Rings" down.

Johnny Depp
The Matrix
According to an interview with Matrix composer Don Davis, Johnny Depp was the Wachowskis' first choice for Neo.

Jean Reno
The Matrix
Reno turned down the role of Agent Smith to do Godzilla instead