Alf (above) doesn't make my list because he's too cute and cuddly. This also excludes E.T. and Starman for the same reasons.

I have also found that extraterrestrials like Martians, Predators, Body Snatchers and Aliens from the movie Alien aren't that interesting because they resemble monsters on the loose that can found in any grade Z horror movie.

However, there is a guy who loves these kinds of aliens and you can find his top ten list here. 

My list contains aliens who have a degree of complexity and cunning concerning their actions.

1. The Q from the Q Continuum: These are fascinating powerful beings who seem to be looking for fun ways to spend eternity.
2. The Grey alien from Area 51 called Paul. He talks and acts like a cool dude from the 1950s and 60s. If only, the other "top secret aliens" were as funny as him.
3. Star Trek's Data: He's an android that took on a life of his own. One of Star Trek's best characters. I loved the episode where he created a child of his own in The Offspring.
4. Klaatu and Gort from "The Day The Earth Stood Still": A friendly alien tries to help mankind, but paranoia follows him around. The robot, Gort is the enforcer against nuclear weapons.
5. The Jedi Knights from Star Wars: These knights are connected to "The Force". The lightside or the darkside. The duality of good and evil influences everybody in the universe.
6. Trafamadorians from Kurt Vonnegut's "Slaughterhouse Five": These aliens are probably the strangest ones ever created. They look like toilet plungers with an eyeball. In the book/movie, they accidently destroyed the universe, then they transported a new Adam and Eve through time to build a new Earth.
7. The visitors in the TV series "V": They're really reptiles disguised as humans. They look friendly, but in reality that want mankind for food and water. Reminded me of The Twilight Zone episode, "To Serve Man".
8. Aliens from the movie "They Live": Wrestler, Roddy Piper discovers aliens who have almost complete control of the human race. Scary.
9. Star Trek's Vulcans: They used to be a violent race, then they became spiritual and logical. "The Vulcan Mind Meld" and "The Vulcan Pinch" were always useful in certain circumstances.
10. Superman: His real name is Kal-El from the planet Kryton. His mission is to protect Earth from evildoers whether human or alien. So far, he's done very well in comic book and movie land.

In attempting to find out who or what is in this huge universe, sci/fi writers have expanded our minds and imaginations off of this dirt ball.

The prospect of meeting real aliens is now on our collective mental horizon.

Our concepts of extraterrestrials are different now from "The War Of The Worlds" mentality of the 1950s.