These horror and suspense movies are out of this world. Or rather, they feature creatures from out of this world coming to Earth to take over. Or at least grab a quick bite to eat. (Note: it's debatable what constitutes a horror/suspense movie, but the "invasion" aspect means them visiting us, not vice versa -- thus, no Alien.)
Honorable mentions: It Came From Outer Space (1953), The Quartermass Xperiment (1955), Invisible Invaders (1959), Goke, Body Snatcher from Hell (1968), Monsters (2010).
25. Invasion (2007)
In this inventive POV film, the takeover of citizens of a small town by parasitic aliens is captured from the dashboard camera of a police cruiser.
24. Strange Invaders (1983)
Part tribute to, part parody of '50s alien invasion movies like Invasion of the Body Snatchers, this little flick about aliens taking over a small town combines decent effects and a nice sense of paranoia.
23. Undead (2003)
An zombie uprising turns out to be caused by aliens in this ambitious low-budget Australian debut from the directors of Daybreakers.
22. Alien Raiders (2008)
In this high-octane thriller, a hostage situation inside a supermarket is revealed to be the work of a group of hunters tracking people who've been taken over by alien parasites.
21. Evil Aliens (2005)
Tasteless but fun British splatter comedy about a conspiracy theorist TV show crew covering the story of a woman supposed implanted with an alien fetus.
20. The Substitute (2007)
In this engaging Danish film, a group of pre-teen students begins to suspect that their substitute teacher might in fact be a malevolent alien...and they're right.
19. Species (1995)
When an alien transmission compels scientiests to splice alien DNA with human DNA, they realize to their horror that the source of the transmission intends for the hybrid creature to procreate and eradicate the human race. Oops.
18. Invaders from Mars (1953)
Fun but melodramatic relic of the time, this precursor to Invasion of the Body Snatchers eventually turns campy when the aliens show up in their green crushed velvet body suits, led by a silver telepathic disembodied head.
17. Signs (2002)
Until the forced ending, M. Night Shyamalan's story of crop circles foretelling an alien invasion is often riveting and surprisingly scary.
16. The Earth Dies Screaming (1964)
When almost all of the citizens of Earth suddenly keel over from a mysterious force, a small band of survivors -- including a pilot who was in midair at the time -- join up to figure out what's going on. Aliens and robots and zombies (oh my) play a part in this atmospheric chiller from iconic Hammer director Terence Fisher.