One of the oldest tropes in science fiction. Hell, you could even make a case that The Iliad is the earliest tale of invading aliens...told from the aliens' point of view. It's also one of the most hackneyed ideas in Hollywood. SF literature has done the idea much, much better (with one exception) - so read these before you write yours:
War of the Worlds, H.G. Wells
“Who Goes There?” John W. Campbell (This novella is the source material of no less than three movie adaptations, all called The Thing.)
The Puppet Masters, Robert Heinlein, 1951
Invasion of the Body Snatchers, Jack Finney 1956
“Come Into My Cellar,” Ray Bradbury, 1962
What was that one movie exception? It's after the jump.
As for the one movie that contributed something new to the alien invasion trope - it's Alien Nation.
Yes, I said it. Alien Nation. It was cheesy, but it had a genuinely new twist on the aliens: They weren't super beings. They were refugees, and they didn't want to be on Earth any more than we wanted them here. And they promptly become Los Angeles' newest impoverished immigrant group. Sound familiar to anyone? Like, say, an acclaimed low-budget South African film of a couple of years back? Just sayin'...