From Sandia is a press release discussing their analysis of the spores
From Dr. Henry L. Niman is a discussion of how some letters only caused cutaneous anthrax, while others only caused inhalation anthrax, strong indirect support for weaponization, since in nature there are vastly more cutaneous than inhalation cases, even in areas where spores are regularly inhaled.
Dr. Barbara Rosenberg presents a detailed and well-referenced discussion of several aspects of weaponization. Unfortunately, I have lost the links she provided, but will try to correct this asap.
An Anonymous Scientist made some salient points as comments to my blog that I'd like to highlight also.