#1: Harry Callahan's S&W 29, .44 Mag. The most powerful handgun in the world.
#2: James Bond's PPK
#3: Indiana Jone's Webley .455 break-top. Especially notable is the
"gun vs. sabre" scene, yet there he carries a S&W MkII
#4: Lara Croft's HK USPs
Yet the most legendary movie guns are still the countless SAA / Peacemakers etc. that epitomize the Western genre as such, even though I have no particular movie or scene in mind.