Daleks (Dr. Who)

Xenomorphs (Alien series)

Predators (Predator series)

Cylons (Battlestar Galactica)

The Borg (Star Trek)

The Goa'uld (Stargate SG1)

Reapers (Mass Effect series)

Martians (Mars Attack!)

Jabba The Hutt (Star Wars)

Invaders (War Of The Worlds)

Bugs (Starship Troopers)

Other: