I'm not sure, but I think this is a first: Digital Manga Publishing is publishing manga on the Nook, Barnes & Noble's proprietary e-reader. (Like all smart e-readers, the Nook is available not just on the device itself but also as an iPad, iPhone and web application.) There are only a handful of graphic novels available for the Nook, mostly indie material; the best known is probably Mike Jasper and Niki Smith's In Maps and Legends, which started out as a Zuda comic.
Digital, which has been in the vanguard of, well, digital manga publishing, with their eManga website and Digital Manga Guild, will launch with Vampire Hunter D, in both color and black-and white-versions, divided into two parts for $3.99 each. It's also available on Kindle for $7.95, and the cheapest way to read it is on the iPhone/iPod Touch, where each of the six chapters in volume 1 is priced at 99 cents. You get what you pay for, though—I read the first volume on the small screen, and it doesn't adapt well. This is a book that needs a little breathing room.