Seems like there are quite a few sites that focus on a green Halloween.
Siel, of GreenLAGirl fame, now writes a column for the Los Angeles Times and recently posted 7 Steps to a Greenish Ghoulish Halloween.
In a similarly ghoulish vein, The Sierra Club's blog The Green Life, offers nine more tips (although the Fair Trade Trick or Treat Action Kit seems to be a common thread).
National Geographic's The Green Guide gets into the DIY business when they suggest Halloween costumes done the old-fashioned way...you maaaake them.
Rounding out the bunch is the Seattle based Green Halloween, with tips for parents, kids, and schools and ideas for "thinking outside the candy box." Okay, let's not go too overboard...