The Day of the Jackal by Frederick Forsyth
A year-zero reboot for the modern thriller. It changed the game in many ways.
The Silence of the Lambs by Thomas Harris
Another game changer. Procedurals were never the same afterwards.
Daddy by Loup Durand
A great chase thriller featuring a precocious boy, Nazi killers and a pack of desperados tasked with protecting the boy, usually at a distance. First rate.
The Damned and the Destroyed by Kenneth Orvis
I bought an imported American paperback in 1969 because of its lurid pulp cover, but it turned out to be a solid PI story set in Canada. I remember it well, 46 years later.
Mr Mercedes by Stephen King
Only he could write a thriller this way.