I'm not sure if this counts, but I say Galactus. You would have a lot of freedom because I think they only showed his shadow in the last Fantastic Four movie.
2. Heimdall from Thor.
3. New Judge Dredd helmet.
the more I see the new judge dredd helmet the more I like it!!:love
My original thoughts was the police helmet/mask off of the latest star trek movie which I think is pretty cool but it only had about 30 sec screen time! lol
I like the Captain Britain helmets I've seen here.
Others:
Ant Man (original)
Beetle (Marvel Comics)
Galactus (may have to be scaled down lol)
Black Knight
Silver Samurai
The Vision
Red Tornado (DC Comics Android) might be able to modify an Iron Man helmet.
Guardsman (Marvel Comics pictured here), I'd really like to have this one maybe have green led's for the eyes.