I just got done reading the first book he wrote.  Great book.  Shame the guy passed on before he could write more than the three books in this series.  Check him out if you're looking for a good read.

http://www.stieglarsson.com/

I read the first 2 and am waiting for my wife to finish the 3rd so I can start that. I read on MSN, or some other site, that they just found another unpublished book of this series. I think they said it was the 5th in chronological order. So I'm guessing that someone has the 4th stashed away waiting for the right price.