1. And Then There Were None by Agatha Christie: I am limiting myself to one Agatha for the purposes of this list, and this is the one, although it's not an easy decision. This book was a high wire act, and Christie pulled it off with apparent ease.
2. Gaudy Night by Dorothy L. Sayers: How could I not pick this one? While nominally a piece of crime fiction, Gaudy Night is really a feminist examination of current society, peopled with brilliant women characters.
3. Presumed Innocent by Scott Turow: while I am not personally a fan of courtroom drama, and I don't think that Turow ever again wrote anything that equalled this book, Presumed Innocent is brilliant and was groundbreaking in 1986 when it was published. It was a blockbuster that set the stage for Grisham's The Firm when it was published 4 years later.
4. Postmortem by Patricia Cornwell: published in 1990, this book is the first in the long-running Kay Scarpetta series, in which Cornwell really leveraged advances in forensic investigation in fiction. This book is incredibly suspenseful and truly scary, and I still remember reading it in bed, terrified out of my mind, unable to look away.
5. The Bride Wore Black by Cornwell Woolrich: a piece of noir mystery published in 1940, this book is riveting and literally unputdownable. The twist at the end is shocking for its cavalier brutality.
6. The Hollow Man by John Dickson Carr: published in 1935, this is a near perfect locked room mystery, with one the best expositions on the appeal of detective fiction that has ever been put to paper. There isn't a word out of place.
7. Brat Farrar by Josephine Tey: a stunning tale of the return of the prodigal son. Is he an imposter or isn't he? There are so many different ways that this book could have gone that watching Tey make her narrative decisions is a master class in plotting.
8. Faceless Killers by Henning Mankell: this was the book that started me reading Nordic Noir, starring Kurt Wallander, a tortured Swedish police detective. This isn't necessarily Wallander's best outing, nor is it Mankell's best story, but I read every single Wallander book I could get my hands on long before the series was a gleam in Kenneth Branagh's eye, and I cried finishing 2009's The Troubled Man, knowing that the Wallander series had come to an end.
9. The Alienist by Caleb Carr: I read The Alienist when I was in law school, and it's at least partially responsible for my long-running love affair with historical mystery. When I read it, I hadn't read anything quite like it, and it felt like it was made for me, with its early New York setting and it's dark, twisted aesthetic.
10. The Hound of the Baskervilles by Arthur Conan Doyle: what would a crime list be without Sherlock Holmes, who spawned an entire genre of detection fiction. The debt owed to Doyle couldn't be repaid in a thousand years, and this short novel is, in my opinion, the most atmospheric and compelling of his work, even if the mystery isn't the strongest.
I'm skeptical that I'll be able to winnow it down, but I may well need to add more. I also didn't make any effort to avoid books that are mentioned in 1001BtRBYD, because I was just thinking about my own "crime canon," and what it would include.