Evil Star
The second book in Enid Blyton's Famous Five series is called "Five Go Adventuring Again."
The fourth book in the Power of Five series is called "Necropolis."
Ravens Gate
As of now, there are no officially announced plans for another book in the "Power of Five" series by Anthony Horowitz. However, the author may choose to continue the series in the future.
It was released in Autumn 2012.
Rick Riordan is writing the first book to the second series, and is said to be released this fall [2010], at the moment there is only five books, but the second series will be out soon. [I can not wait!]
Autumn 2012 (October)
five, though there is a first book, second book, third book, into the mist, and the fourth book.
They all have different names. The first series is called the Original Series, the second is called The New Prophecy, and the third The Power of Three. Erin Hunter is coming out with a new series called the Omen of the Stars. There is only one book out yet in that series which is called The Fourth Apprentice. I think you're talking about a series as in trilogy, saga, or quintet. I don't know the name of anything other than that, but I just wanted to clear that up.
The Power of Five series has the following books:Raven's GateEvil StarNightriseNecropolisOblivion
The fifth Power of Five book will be released on the 4th October 2012 and will be called Oblivion
Series One or Series Five.