Bouncing off the Fine Books & Collections preview, Forbes has a profile of the most expensive books of 2006, noting that records were set for atlases (the 15th century Ptolemy for $4 million); French literature ($644,000 for a signed copy of Rimbaud's A Season in Hell); and Australian books ($689,000 for Journey of Discovery to Port Phillip, New South Wales).
As noted previously, the 2006 "top ten" includes five atlases. The Forbes piece is accompanied by a nice photo slide show.