The folks at Evil Mad Scientist Labs have put up a number of cool Halloween projects, including this Flying Spaghetti Monster costume (I think I just figured out what I want to be this year). They also have an LED pumpkin, Headless Horseman LEGOs (with LED eyes) and other how-tos. Here's a link to the Halloween Projects page.

EMS Labs will be at Maker Faire Austin showing how to make high-tech pumpkins and the umbrella bat costume.

Make a Flying Spaghetti Monster Costume - Link