1 -The Alien alien
The acid for blood xenomorph, that plagued Ripley to her death and subsequent refusal of motherhood to the matricidal weird-ass-alien-human-hybrid thing that got sucked out, from the inside-out, of their spaceship on their re-entry to earth after being genetically rebuilt for the forced, sorry, fourth instalment of the series, is just bloody well epic! It's changed, evolved if you will, along the way but it remains to this day the most terrifying son of a bitch EVER!
The iridescent John Hurt showing the world how to act everyone out of a room, including the chest burster!
2 - Spock (Whose surname is unpronounceable by the human tongue - get him right?!)
The Half-Human, Half-Vulcan Kick-Ass Machine of Awesome rocked his way through time and space making no apologies for his logical daily fist pumping advice. He is one of the Holy Trinity of Star Trek and can make even the sturdiest of folk go floppy all over with the touch of his Vulcan Nerve Pinch! Get in!
3- Superman/Kal El
The man of Steel! Nuff said really; 'cept maybe HE BE EFFING DEADLY!
But seriously, whether you know the alien as Superman, Kal El, or Clark Kent (or Last Son Of Krypton, The Man of Tomorrow, First Citizen of Metropolis, Big Blue, The Metropolis Marvel, Gangbuster, The Big Blue Boy Scout, Superbaby, Superboy, General El, Commander El, Nightwing, The Ghost, Superman Red, Superman Blue, Nembo Kid, Action Ace etc. One assumes he has severe "Tax Problems") he is the hero of heroes. Flying to the rescue of whomsoever needs him, and he knows you need him because he can hear you. Like Santa, he has great hearing! Unlike Santa, he can shoot solar energy from his eyes, leap buildings in a single bound, have bullets bounce off of him, can see through things excluding lead but including your underwear! Basically he ticks all the boxes, but sadly he was in Superman 3 + 4 and they're reason enough to get anyone banned from the top two!
4 - Gordon Shumway
A brown, adorable, fluffy alien from Melmeck nicknamed ALF by the family whose garage he crash landed in. He becomes a member of The Tanner family, acclimating himself to the cultures of earth, through 102 episodes. He also got animated in 1987. He likes to eat cats and is as cute as a button, a button with a deep soothing voice and hands with the ability to destroy you!
5 - Frank N Furter
Frank, the cross dressing, genius scientist from Transexual Transylvania, just wants a man to love. Or a woman to love. Or Meatloaf to love, for that matter. What I'm trying to say is, even aliens want love. Except for the Pod People. They just wanna replace the hell out of you!
6 - The Body Snatchers from Invasion of The Body Snatchers 1956's VSN
The Pod People have had many incarnations but Bob Siegle's is the ultimate! The sneaky space seeds drifted through space and time until they came upon earth ridding us of, well us! On the upside though emotions become a thing of the past and we know what pesky brats they can be!
7 - ET
The little dude has a retractable kneck, a glowing finger and huge eyes that make Bambi look like a chump!
8 - The Brood from The Uncanny X Men
Jeez these things frightened the innocence out of me so they did.
Notable Mention - The Alien what Lazer Zapped The Valley Chicks in Nowhere! This chap was a pleasant aul fellow 'cept for the lazering that is, but sure the world could only be a better place sans Rose McGowan, Shannon Doherty and Traci Lords' characters, not them themselves obviously, sure it would be a sad day if them lassies were dead. And let us be honest the real reason I'm mentioning this alien is so I can Get Nathan Bexton's picture in my list! Boom!