The choice is obvious to me. A Headcrab. facing the same direction as the head (that is supposed to be a head, right?), have its fangs extend downward onto the forehead area, and then the legs could wrap around the sides of it. I think it could look really good if the Headcrab was highly stylized to fit in with the rest of the design.
Here's a shitty little thing I made in Paint to show what I mean:
If you could just smooth out the edges of that and let the lines flow a bit more with the outline of the head, I think it'd look pretty good.
I have to say though, that head doesn't exactly lend itself to the theme of the game.