Pretty soon. In about a year, I can tell you that.
I wonder when you wrote this, because Percy Jackson and the Olympians series are finished. There's a new series with the same characters and a few new ones, that's called the Heroes of Olympus. The last book in the series are coming in a month or so. Read it if you haven't; there's an awesome character named Leo Valdez in it.
He is not making a new series based upon the Olympians next. Next, he is making one based on egyptain gods. The new series is called the Kane Chronicles, and the forst book is alerady out. He made The Heroes of Olympus series.
Frankly, there is no series after the Percy Jackson and the Olympians after it is already complete.
The Heroes of Olympus was the next related series.
The first book is Percy Jackson and the Olympians, the Lightning Thief The second is Percy Jackson and the Olympians, the Sea of Monsters The third is Percy Jackson and the Olympians, the Titans Curse The fourth is Percy Jackson and the Olympians, the Battle of the Labyrinth The fifth is Percy Jackson and the Olympians, The Last Olympian You can also get The Demigod Files and other supplement books.
I think Rick Riordan concluded the Percy Jackson and the Olympians series. I don't think a book six will be coming out. Percy's story is continued in the Heroes of Olympus series with the book, The Lost Hero.
Not in the Percy Jackson and the Olympians series, but there is another book coming out...not 100% sure when.
The Percy Jackson Camp Half-Blood series ended with the fifth book, The Last Olympian. The next series came out, The Heroes of Olympus. Percy plays an important part in the series, although he is no longer the main character.
The main character in the next Percy Jackson and the Olympians series is named Jason. There is not much information given on him, or the next Camp Half blood series.
No information on the 6th book has been released yet.
Sadly, there are no more books in the series after book # 5, The Last Olympian. But Rick Riordan will be making a similar series about demigods. Of coarse, the books won't exactly be as precious as the Percy Jackson & the Olympians series, but atlest it's something.
It is coming out around Fall 2010 at least that is what people are saying -Peace- *Bananaz*