Three breasts. Don't ask why :)

I dunno, I think part of it for me is the sort of otherness that you get from most sci-fi aliens. Kinda 'human, but.' Big fan of tails and markings, and also a fan of strange body types that aren't mimics of earth creatures. The quadruple jointed legs from that one species from Titan AE, for instance.

A short answer would be my new OC I'm working on:

http://www.furaffinity.net/view/13218667/

maybe she'll give you some ideas! :3

Hell yea to Uratoh's pic.

I know its what they are working with (as in actors in suits) but most scifi series and films have basic humanoid aliens with different colour skin or little antennas to show they are not human and this just disappoints me.

To me aliens should be more like Alien the film or Lickers from resident evil. Combinations of some or all the following (Sorry its a bit ranty and disjointed). Big gribbly things with tendrils and spikes, maybe more legs than necessary, dribbling acidic venom, chitinous armour, impossibly articulated (Like you have it pinned down just for it to rotate its arms legs and/or head in an unexpected way so now your the one pinned down)mouths with big sharp teeth not always in the expected place (Like an octopus envelops its food and sucks it in). Yea wheel they are just the first random thoughts that came not my head.