After you have finished the New Jedi Order and Dark Nest audio books, you may want to check out some of the other Star Wars books.
A good place to start would be the Thrawn Trilogy by Timothy Zahn. This series is set after the events of Return of the Jedi, and follows the rise of Grand Admiral Thrawn. These books are widely considered to be some of the best in the Star Wars Expanded Universe.
another option would be the X-Wing series by Aaron Allston. This series focuses on the Starfighter pilots of the Rebel Alliance, and is set during the same time period as the Thrawn Trilogy.
For something a bit different, you could try the Young Jedi Knights series by Kevin J. Anderson and Rebecca Moesta. This series is aimed at a younger audience, and follows the adventures of a group of young students at the Jedi Academy.
There are many other great Star Wars books out there, so feel free to explore and find the ones that you like the best!