As far as spy novels, all of Robert Ludlum’s early stuff is great. Very entertaining. Also Len Deighton’s ‘Bernard Samson’ series of 9 books is excellent.
Other authors to check out (not “spy” genre) are Michael Connelly, T. Jefferson Parker, and James Grippando. All are consistently solid and entertaining.
You might also check out Stephen Frey. He writes Wall Street thrillers, also very entertaining.
Other authors I have enjoyed are:
You won’t go wrong with any of them.
Good luck, and happy reading!
John Sandford is terrific also.
I read his latest,along with Michael Connelly’s just last week.