Non-photo blue pencils (available at art supply and office supply stores by special order) are used quite often in the comic book industry.

You can purchase pre-printed comic book boards that have the page outline, guidelines for panels and boxes for text inked in the same non-photo blue color.

From the original art panels I've personally seen, it appears that letterers use it extensively. Guide lines can be drawn for the letters to make them straight and even, and the lines will not reproduce when the pages are sent to the printer. Some artists use it to block out panels, then pencil in the details.

Most of the colored pencil manufacturers (like Prismacolor) sell versions of non-photo blue pencils. Jerry's Artorama carries them for 95 cents each, and Office Depot carries them by special order, $3.99US per dozen.