In some of The Saint's novels Simon Templar had a girlfriend, Patricia Holm. However, there was no such character in The Saint show. Who, in your opinion, of all TV and movie actresses of that time, English and American included, could have played the part?

Well, three actresses spring to mind who appeared in more that one "Saint" tv show, and their chemistry with Roger was always excellent.

They are: Justine Lord, Annette Andre and Suzanne Lloyd.

I like your third choice the best. Of all the ladies who appeared in The Saint, I'd also add Sue Lloyd to the list. (Funny, isn't it, how Susanne and Sue both have the same last name and first names are so close?!)
Going back to your three choices, I think that Susanne Lloyd could play very intelligent, sassy and spunky characters, and at the same time take on weaker female roles as well. She was quite an actress in her day. I saw her in "Zorro", the late 50's Disney TV series, and she played a bad gone good person and was very good either way.  :smt001 Sue Lloyd, imho, had the kind of quality that made it hard to imagine her playing a ditzy girl. She looks and acts too intelligent for that. Wasn't she also a spy in Michael Caine's "Harry Palmer" movies who got involved with Michael Caine's character?  

But Justine Lord to me was a bit on a ditzy side.  :smt002 I can't quite imagine her playing the Saint's sidekick. What do you think?

Yes, Justine Lord was always a little on the scatty side!

I would choose Shirley Eaton, great actress, and I enjoyed all the Saint shows she did with Roger.

Watching another episode yesterday with Suzanne Lloyd got me thinking that while I like her a lot, she seems to be in more episodes than all other female guest stars on the show. Most of the characters she plays are similar and it gets confusing because she plays a different one in each episode. Do you think that she was a little overused in The Saint?

Roger was asked once why the same actors kept cropping up in "The Saint" and he replied that if the actor was good, worked without fuss, and got along with everybody, then they were happy for them to return back to the show. Maybe Roger got along very well with Suzanne, and they did have a certain chemistry together. Though I always preferred it when Annette Andre was co-starring. They were very good friends, and Roger has been quoted as saying "Let's have Annette back to liven things up."

Yeah, they probably had to fit this in with the budget, too, or how many shows they promised an actor/actress by contract  :smt017 . Another example of budget would be repeated use of sets, which would also get confusing when Simon appartment would turn into something completely different in another episode. But even if Suzanne was easy going and got along with everyone, I think she appeared in a lot more episodes than most other guest stars, even compared to Annette.  :smt061 Do you know if she is American? I saw her in several other American series, like Zorro, for instance, as I mentioned earlier.