Ok, here's my attempt.
Pretty. This is why I stick to mapping... XD
Though I'd find them hard to figure out easily at 'first glance'. IE: You've really gotta stare at Alien and Human technology to see the difference.... which defeats the point of a 'quick icon' for reference. Not sure if you'd lose the niceness of the images by using slightly different shades, or colors, or something that helps the image stand out?
I played with this a bit because the eyes didn't come across. I also changed the shape of the head a little and removed the nose:
I think maybe the eyes would look better black.
Works for me... Mine kind of looked like a frog in headlights and couldn't figure out how to get the pupils across... ignoring them outright worked well.
Since Bly's leaving for 2 weeks, I wouldn't be insulted if my icons are placeholders until Blywolf can produce a 'final, polished, finished' set, BTAxis. I just wanted to take a stab at it.
I already know Graphic Art and me have a long way to go before what I produce is better then average.