Potentially the greatest ever blog in the world is Laura Hudson & Leigh Walton's Cereblog, in which they are going to read and blog about every issue of Dave Sim's Cerebus. This would be totally awesome if they were reading each issue for the first time ever, but sadly they seem to be broadly familiar with the title.
For those of you not in the know, Cerebus ran for three hundred issues. Dave Sim initially wrote and drew it alone, but later he was joined by Gerhard on backgrounds. It tells the story of Cerebus, and aardvark in a world of humans. Initially it was a light-hearted and somewhat throwaway pastiche of then-popular Conan The Barbarian comics, before gradually mutating into something considerably more ambitious but then annoying everyone by becoming a reputedly unreadable vehicle for its writer's increasingly crankish opinions. In its period of greatness it was one of the best comics ever written, and if it had maintained that level of quality to the end it would be talked about as one of the greatest art works of all time.
With thanks to Popular Tom for pointing me at Cereblog.