Here's what wikipedia has to say:
Quote:
Plans
The manuscript for the fifth volume is half-written as of May 2005:
* A Dance with Dragons
In a May 2005 statement, the author estimates that the series will require seven volumes. This is an increase from previously stated figures because Martin had to move some of the character arcs of the A Feast for Crows manuscript into A Dance with Dragons, due to the fact that the manuscript already exceeded the length of A Storm of Swords, which itself had to be split into two halves for several markets. Martin recognized that this decision could cause frustration among some of his fans. He wrote: "I know some of you may be disappointed, especially when you buy A Feast for Crows and discover that your favorite character does not appear, but given the realities I think this was the best solution... and the more I look at it, the more convinced I am that these two parallel novels, when taken together, will actually tell the story better than one big book." [1]
Martin originally intended the series to be a trilogy, but later increased that estimate, remarking, "What can I say? It's a BIG story, and a cast of thousands." [2] When A Storm of Swords was published, Martin announced that there would be six books. After A Storm of Swords, he began writing A Dance with Dragons, which was intended to take place five years after the end of A Storm of Swords without the use of many flashbacks, much to the dismay of many fans. However, he later announced that the five-year gap wasn't working, and therefore he would add another book, A Feast for Crows, to pick up where A Storm of Swords left off. Interestingly, his decision to stop writing one book and start another in order to chronicle part of that five-year gap is responsible for a five-year wait for the fourth installment.
Projected titles for the sixth and seventh books are A Time for Wolves and The Winds of Winter, respectively.