The Boy and the Beast by Dira Sudis
This is perhaps, my very favorite Sterek fanfiction.
The Summary:
In which events in Beacon Hills go rather differently from the start, and a Beauty and the Beast (ish) story ensues. (Scott is not a teacup and no one sings about their feelings.)
What I loved most about this book is that it has such a slow build. It starts off with Stiles getting into trouble at the old Hale House and Derek coming to his rescue.
The best part of this is that the characters are still true to the show, yet we have a completely new plot. So many times in Sterek fan fictions while the stories are original, they really end up just being smut with no logic or plot. But this is actually a very good, very original strong story.