Keith R.A. DeCandido, author of Supernatural: Nevermore, has posted details on the upcoming, and third Supernatural tie-in book, Bone Key.
Supernatural: Bone Key is due for release on September 2008.
The new book will take place shortly after A Very Supernatural Christmas, as Sam, Dean and Bobby are heading to Key West, Florida. It seems that the brothers, as does Bobby, don't appear until the third chapter.
Source: Keith R.A. DeCandido LiveJournal.