The latest version of the Cybermen on Doctor Who looks sleek and pretty cool... but they could have looked more insectoid and shown more of their former existence as organic humans, if this concept art from Millennium FX had been used. Check out that horrible mouth! (Click to embiggen, it's worth it.)
The above image is one of a few concept art pieces that came out in a new "showreel" about the Cybermen from Millennium, via Radio Times. Here's another one, showing a weird external circulatory system and a more 1960s-influenced face design.
And here's one more:
As I mentioned, these images come from a Cybermen-themed "showreel" released by Millennium FX, which does a lot of the VFX work on Doctor Who these days. The video also includes some footage of a person being put into Cybermen armor, which involves a lot of clay. Here's the whole video, which was posted by the Radio Times: