My husband and I enjoy the Jack Reacher series by Lee Child (fast paced novels about an ex-military police officer which remind me a bit of the old "Fugitive" TV series), and the Harry Bosch series by Michael Connelly (Bosch is former military, currently an LAPD detective). In my opinion Michael Connelly is the better writer of the two, but the Reacher novels are a good ride!
Another idea is buy him a gift certificate with recommendations -- that's what I'd do!
Sorry, my suggestions aren't properly "spy" thrillers, but I bet he'd like them! For classic spy thrillers, John LeCarre as mentioned already. Also look at Robert Ludlum, Frederick Forsyth, and Nelson DeMille.
Good luck, and have fun!!