Here's my halloween 2009 costume for my son.
My son wanted to be the original 'Alien' from Alien. This is the original H.R. Giger Alien, not the various other shapes it morphed into in the sequels.
It doesn't appear I have the right permissions to upload pictures yet, so I'll just point you at the source. It has a movable jaw and motorized tongue. I wrote down fairly detailed build instructions. Love to hear what you think!