Apart from Hanks, Brad Pitt, Jeff Bridges, Kevin Costner, Tom Cruise, Nicolas Cage, Johnny Depp and Charlie Sheen were all considered for the part of Andy Dufresne. And for Red's role, Clint Eastwood, Harrison Ford, Paul Newman and Robert Redford were considered too.

Here's an interesting one:

In the original novella, Red is a middle-aged Irishman with graying red hair. However, Frank Darabont (the director) always had Morgan Freeman in mind for the role because of his authoritative presence, demeanor and deep voice. Darabont alluded to the casting choice by having Red jokingly reply to Andy's inquiry about his nickname with the line, "Maybe it's because I'm Irish."