I didn't think Kobo price-matched for books that are free, but apparently they do because The Sixth Discipline is now FREE on Kobo! I updated the Free eBook page (see tab above right) to include it. That means the book is now free almost everywhere!
Kindle (US only)
Nook (Barnes & Noble)
The only exception is the Sony ebookstore, which seems to take forever to change anything (and they still don't have my fifth book Shades of Empire, either!).