I stumbled across this post by accident, but it is fantastic. Apparently, Mattel issued a Halloween Barbie doll every year starting back in 1997, and they look amazing. My personal favorite is the Trick or Chic Barbie from 2008 which manages to look like she is wearing an incredible Halloween costume while still being Barbie fashionable. You can’t beat that.
For the entire list visit the Fashion Doll Guide (a great site beyond just Halloween stuff.)