A few more besides
David Bauer (Morton Slumber, DAF/ US diplomat, YOLT)
Michael Goodliffe (Chief of Staff - uncredited - in TMWTGG)
Eunice Gayson (Sylvia Trench, DN & FRWL)
Joseph Furst (Dr Metz, DAF)
Martin Benson (Mr Solo, GF)
Bryan Marshall (RN submarine commander, TSWLM)
Hal Galili (one of the mob bosses in GF)
Bill Nagy (another one of the mob bosses, GF)
Eric Pohlmann (the voice of Blofeld, FRWL & TB)
Anthony Dawson ( Professor Dent, DN, the hands of Blofeld, FRWL & TB!)
Marne Maitland (Lazar, TMWTGG)
Douglas Wilmer (Fanning, OP)
John Hollis ("Blofeld" ? in FYEO)
Joe Robinson (Peter Franks, DAF)
Bruce Boa (USAF General, OP)
Ed Bishop (Hawaii control, YOLT, Klaus Hergerschimer, DAF)
Clive Cazes (the unfortunate Spectre 9 - electrocuted but uncredited! - TB)
Robert Hutton (Presidential aide, YOLT)
Burt Kwouk (Mr Ling GF, Spectre agent, YOLT)
Edward De Souza (Hussein, TSWLM)
Cec Linder (Simmons, GF)
Jack Hedley (Havelock, FYEO)
Vladek Sheybal (Kronsteen, FRWL)
Cyril Shaps (Markowitz - or was he Bechman? in TSWLM)
Terence Rigby (Russian general, TND)
Peter Madden (McAdams, Kronsteen's chess opponent, FRWL)
George Pastell (Train conductor, FRWL)
Bernard Horsfall (Campbell, OHMSS)
Nadia Regin (Bonita, GF)
Valerie Leon (appeared in TSWLM and NSNA, I think)
David Healy (mission control in both YOLT and DAF)
Vernon Dobtchieff (Max Kalba, TSWLM)
George Roubicek (astronaut in YOLT, Stromberg sub commander in TSWLM)
Geoffrey Cheshire (Toussaint in OHMSS)
Francis de Wolff (the gypsy chief in FRWL)
Rose Alba (appeared in TB, I think)
Steven Berkoff (General Orlov, OP - he was in the Saint episode I watched on Sunday!)
Philip Locke (Vargas, TB)
Of course, it helps if you've got the boxed sets of The Saint and full cast lists! That's all I can spot, so far, over and above the ones already mentioned! 
(PS - sad, I know, but I've just thought of one more - George Murcell, Russian diplomat in YOLT. Murcell played a "Blofeld-lite" character in The Saint named Vogler - the villain in an episode called "The Death Game", supposedly killed off by Simon Templar at the end, only to reappear a few episodes later in "The Power Artist".)