I only have four because I while I have read more than four, these series are by far my most favorite series I have ever read.

Harry Potter- I would love for this series to continue on so that way we find out what exactly happened to Hogwarts.  Another reason why I wish this series had more books is so that we could read about what the offspring experiences at Hogwarts were like.

The Chronicles of Narnia- I would love to read more Narnia books just because those books took me to other places in my imagination.

Divergent- I loved this series and hated how Allegiant ended.  I just want more.

Lord of the Rings- This is another series that I just want more of.  Like I wanna know if Aragorn and Arwen had kids, does Frodo ever recover during his time in the Undying Lands?  This is why an extension of the series would be amazing!!