Diamond Comics, who distributes books, mostly to specialty comic shops, has collated their sales data into a list of 100 best selling books of 2012. Being that this is Diamond, there are several qualifying factors, including that a lot of book stores and online outlets don't get their manga from Diamond, and that it's their definition of "manga," so material like Adam Warren's "manga styled" Empowered get spots.
Too bad Hunter x Hunter isn't listed :/