The Seven Year Itch
The white halter dress, of course! So many celebrities have tried to emmulate Marilyn in that dress... Madonna, Scarlett Johannsen, Gwen Stefani, Courtney Love.
Beetlejuice
Winona's gothic look.
Chicago
I remember the flapper look came back for awhile after this came out.
Plus a bunch more that have already been mentioned... Breakfast at Tiffanys, Roman Holiday, Dirty Dancing, Romy and Michelle, Almost Famous, Desperately Seeking Susan.