Published twelve years after Children of the Mind, Ender in Exile revisits Ender's life between Ender's Game and Speaker for the Dead. Chapter 15 of Ender's Game is further fleshed out, and we meet Randall Firth who helps connect the story to the Shadow series. Although storywise it takes place after EG and before SftD, there are numerous allusions to the Shadow series, so read this book after you have finished at least Shadow of the Giant.
There is also an excellent comic adaptation by Aaron Johnston that explores some of what was left out of the Ender's Game: Command School series, specifically the Hive Queen story.
Pieces of four of OSC's online short stories ("Ender's Homecoming," "A Young Man with Prospects," "Ender in Flight," and "The Gold Bug") appear throughout this novel. Each of the stories can be read in its entirety on OSC's InterGalactic Medicine Show website.
My favorite part of Ender in Exile is the relationship with Ender and Admiral Quincy Morgan. We again to see Ender's unusually quick mind at work.