What do you like?
Old school spy novels: Frederick Forsythe, John Lecarre, Robert Ludlum
Modern Spy: Daniel Silva, Vince Flynn, Frederick Forsythe
Adventure: Ken Follet
African adventure; Wilbur Smith
Detective/adventure: Lee Child
Detective/Britian: PD James
Detective/Russia: Tom Rob Smith
Special Operations: Andy McNabb (stick with his non-fiction)
Humorous Adventure: Donald Westlake, Carl Hiaasen
Sci Fi: Larry Niven, Fred Saberhagen