In a recent article I came across this image:
It says that Loki is using an artifact called the "Tesseract". The word tesseract is just another word for "cube". Therefore the Tesseract must be the Cosmic Cube.
But when I searched "Tesseract" on Marvel.com it linked me to this web Page about The "Dimensional Envelope"
http://marvel.com/universe/Dimensional_Envelope
If you read the Document, it tells us that the Dimensional envelope was a place were Nova and Cosmo trapped a villain named Abyss and an group made up of many aliens named the Luminals, and while in the Dimensional Envelope Abyss defeated The Luminals and TRANSFORMED THEM INTO HIS OWN ZOMBIE ARMY.
So I am claiming that Abyss' Zombie army is the Alien army in The Avengers. Now I will tell you why this seems to be the most legitimate answer.
1) It will explain Loki's interest in the Cosmic Cube.
2) It would explain that the giant portal in the sky is the opening to the Dimensional Envelope.
3)The Aliens have an uncanny resemblance to the Zombie Army in the Comics, and it would explain why the aliens differ from each other.
Their rocking the same headband!
4)It would also explain where Red Skull went when he touched the Cosmic Cube.
5)Also the fact that Marvel linked Tesseract and Dimensional Envelope together on their website must mean they are trying to hint at something.
6)And last but not least, Abyss and his army have had their conflicts with the Guardians of the Galaxy, the Inhumans, and Nova, so this may be the connection to the upcoming movies, and the comics Marvel has been trying to get into the cinematic universe
I think it is pretty legit. Let me know if you agree of disagree down below.