This year, Bindlestiff and I went as the The Black Plague for Halloween. I was a plague victim and he was a plague doctor.
Plague victim: Medieval dress and Venetian style mask with boils. The mask was made by taking a blank mask, forming the features out of salt dough and crayola model magic, and then covering the whole thing with papier mache and painting it.
Plague Doctor: Bindlestiff made his mask using these instructions: http://creepypasta.wordpress.com/2009/05/28/plague-doctor/
The coat was a thrift store trenchcoat. I sewed his wimple using these simple directions: http://slumberland.org/sca/articles/how_to_make_a_wimple.pdf. The stick was made from a dowel, tapered at the end by sanding and then painted black. The hat was shaped out of cardboard and then he glued black felt to it.
How do we know these were good costumes? We made several children cry with them!