The Sixth Sense (1999)
If Willis' characters in the '80s were all about cunning and bravado, the late '90s and 2000s frequently found him in a more introspective mode, especially in this hell-of-a-twist blockbuster from M. Night Shyamalan. (The two would reteam the next year for another supernatural thriller, Unbreakable, in which Willis is also very good in a low-key way.) Willis is the ghost at the center of this ghost story, a child psychologist working with a little boy (Haley Joel Osment) who, famously, sees dead people. The muting of Willis' action-star persona is what's so effective here; his quiet melancholy adds to the chilly mood.
In picture: Bruce Willis with co-star Haley Joel Osment.