It has not yet been released but there is going to definitely be a 4th book. He has announced a while back that he already has 100 pages. Each book seem to have a 2-3 year time span before they were released so it is probable that the 4th one will be made sometime between now and 2014. That is only a hypothesis depending on what he is trying to fit in the 4th book.
Christopher Paolini's fourth book is called Inheritance.
Christopher Paolini originally made it a trilogy but at the end of book 3 (Brisiner) he says there will be a fourth book.
Shur'tugal after Galbatorix's Dragon :)
November 8, 2011.
November 8th 2011
it will be "inheritance"
2010, that's all i can tell.
it is being released on November 8 2011
Christopher Paolini wrote the book Inheritance.
I am not positive, but I think sometime during October 2010 or February 2011.
he has written about 200 pages and may complete it by October
If you are talking about the third book, it is "brisingr" and is already out. But if you are talking about the fourth, its name is yet to be announced let alone when.