[Originally posted at Slacktivist (page 9).]
[Something I forgot to add to this list.]
I left out the one where the upcoming alien invasion of earth causes the various alien groups already on earth to band together under the wise council of whoever from each group happened to be in the area at the time (and one human grabbed to represent humanity) they steal an alien warship and fight the evil invaders.
Invaders operated on a three step process:
1 Send a scout ship, if the planet looks like a good target call for the war ship.
2 Send warship to subdue a city as a means of gauging the defenses. If things look good call in the armada, if not leave (though some or the friendly aliens think this possibility is more rumor than anything else) unless things met a certain level of badness in which case destroy the planet (or at least it's ability to sustain life) from a safe distance.
3 Send Armada, take over planet.
The protagalien's plan is to wait until after the warship calls in the armada, and then steal the warship.