I have been trying to remember all the times the skull is mentioned or shown in the EU.
For games we have the Raven and a Lurker's multiplayer skin on ACM, on Isolation we can see the skull depending on the light. There is of course AVPGalaxy's #skullteam skin from AVP2010.
In the comics the most recent is on Gibson's Alien 3. And I don't remember others apperances, most aliens in comics look quite generic.
In Novels:
"The creature's enormously long skull was actually translucent on the top and I could see right through to a complex row of arched inner segments that didn't look like brain tissie, but like more skull".
- DNA War, pg. 127.
"There was a skull buried inside that head, and he could see the hollows where eyes should have been leering at him."
- Sea of Sorrows, pg. 150.
Who remembers more?