The War of the Worlds
Possibly the single most influential science fiction work ever, there is hardly an idea or theme in H G Wells' seminal alien-attack novella that hasn't been plundered by other entries in the genre. The concept of aliens as a malign, invading force has been used so many times it has become a cliché.
Even the notion of the invaders suffering an ignoble, terrestrial end (in The War of the Worlds, the Martians are finally killed by the humble microbe) has been recycled, notably in Mars Attacks! and Signs. The imagery of the invading tripods has been raided for the AT-ATs in The Empire Strikes Back, The Matrix's sentinels and, of course, the TV series The Tripods. In other cases, Earth's resistance, as hinted at by the artilleryman in an alternative ending written by Wells, is used in V, Battlefield Earth and many other films and TV programmes. The novel has been made into a legendary radio play, numerous films, a musical, comic book series and a TV sequel - and still remains the archetypal depiction of an alien invasion.