TMST: Your favourite series you'd like to see revisited or a spin-off?

Question: What are some of your favourite series you would like to see revisited or a spin-off?

This is a difficult one for me for one of my absolute favourite series ever that ended last year has a spin-off/related series... And the authors have hinted at more to come in future. 

I'm talking about the Kate Daniels series by Ilona Andrews.

It's missing the final book cover but I was lazy and didn't go back and change it... Sorry.

I love it!

The spin-off series is The Iron Covenant series featuring Hugh and as I said the authors have hinted at more spin-offs to come so I guess I'm hoping that those other related series actually materialise at some point in the not so distant future!

I'd love a Roman spin-off or a Julie/Derek Spin-off... Or both because I'm greedy that way!

Another series that left me gutted when it ended was The Hollows series by Kim Harrison.

I'd have legit pimped out a kidney to get my hands on more books in this world but I discovered only a few weeks ago that that would not be necessary as the author is returning to this world, and these characters, and I'm so beyond excited I do a little happy dance whenever I think about it. 

Richelle Mead's Dark Swan series

Anyone who has read this series knows the ending is awesome with the exception of one very big, ugly, and unforgivable thing that immediately needs correcting!

Seriously, thinking about it just fills me with rage!

The author needs to write another book because the series is awesome, and she's said she hopes to write another book for the series at some point, so I really hope if/when this happens the big ugly thing is finally resolved!

What about you? What series do you need more of?