Often overlooked by modern viewers as grade-B 
science fiction, 
The Invasion of the Body Snatchers is a classic 
horror film released in 
1956.  The subversive nature of the alien invasion is typically understood as a reaction to the paranoia of the time, but the exceptional plot and acting make this good watching even by today's standards.
All Wikipedia text 
is available under the 
terms of the GNU Free Documentation License