Looks like the 6th Harry Potter book, "Harry Potter and the Half-Blood Prince," will be available in your local book shop on 16 July 2005.

“We are delighted to announce the publication date [16 JUL 2005]. J.K. Rowling has written a brilliant story that will dazzle her fans in a marvelous book that takes the series to yet greater heights. Harry Potter and the Half-Blood Prince delivers all the excitement and wonder of her best-selling previous Harry Potter novels.”

I still rank the 4th book, "Harry Potter and the Goblet of Fire" as my favorite in the series.  I hope the movie version doesn't disappoint either.
-Chris