Book Five, entitled A Dance with Dragons, is currently being written by George R.R. Martin. As of 24 January 2006, this book consists of 542 manuscript pages (out of 1200-1300 planned).
The novel is confirmed as featuring the following POV characters:
Daenerys Targaryen
Jon Snow
Tyrion Lannister
Davos Seaworth
Bran Stark
Arya Stark
Asha Greyjoy
Theon Greyjoy
An unnamed new POV
An unnamed prologue POV
Theon was not mentioned by name but GRRM stated that an old POV would return and with Eddard Stark definitely dead and Cat confirmed as not having a POV again in the series, that leaves Theon as the only possible candidate.
A Dance with Dragons will take place simultaneously with the events of A Feast for Crows, covering events in the North, on the Wall, in the Free Cities and in Slaver's Bay. The book will feature a map of the Free Cities.
GRRM has commented that it is possible that he may have some room at the end of A Dance with Dragons to drop in some of the characters left hanging ( ) at the end of A Feast for Crows and resolve their cliffhangers from the prior volume. This is only an idea at the present time and is not confirmed. However, the timeline of A Dance with Dragons will likely extend beyond that of A Feast for Crows.
In the publication note at the end of A Feast for Crows GRRM stated that he hoped to release A Dance with Dragons in 2006. That no longer seems feasible and more recently he has suggested a 2007 release date. Amazon is listing a Feburary 2007 release date, but this is only Amazon's guess. No official release date has been confirmed and will not be until the book is finished.
Please check the following site for updates from George R.R. Martin directly on the state of the novel. The next planned update will hopefully be at the start of April.
http://www.georgerrmartin.com/nextbook.htmlBefore anyone asks, Book Six has the working title of 《The Winds of Winter》. No other information is known about it, save that GRRM hopes to have all of the major characters together in one book again.