Funeral in Berlin.
A more realistic film than most of it's contempories. Harry Palmer travels by bus! No sports car, a bus.
The Ipcress File is good too, but not as good as Funeral.
Also the book of By Dawn's Early Light - I thought it was great, and was geared up for watching the film scheduled to be shown on TV but then either Desert Shield or Desert Storm kicked off and it wasn't shown - I've still to watch it