Check out this ForteanTimes article The Science of Aliens. (Register or use BugmeNot.) It’s based on an exhibit from London’s Science Museum and talks about the cool stuff that’s scientifically possible with some hat tips to aliens from our own culture.
BTW, check out the exhibit’s game page where you can see What Type of Alien You Are. (My results: “You’re a hyper-intelligent alien. You would sooner gnaw off your own arm than miss an opportunity to swing your vast intellect around. Immense, sarcastic and fluent in Klingon, you’re a big hit with the opposite sex…but only on-line.”)