It appears that police and firefighter costumes are the winners this year. Challengers are Spider-Man, Josie & the Pussycats, Batman, the Power Rangers, SpongeBob Squarepants and Scooby-Doo.
In Brazil Osama bin Laden is winning over challengers Yassir Arafat and George Bush. Of course he has an unfair advantage, being a ghost too.
It's late in the game, but you can find lots of masks here. This outlet in the UK has a Saddam Hussein mask.
These are scary.