If we're still talking about Standards/Songs that stand the test of time, I think - "I'll be Seeing you" (music/Sammy Fain,lyrics/Irving Kahal) is one of the most moving, beautiful songs I know.

I don't know of it's "overall popularity" compared with songs like Summertime, All the Things You Are, Teach me Tonight etc etc, but I sincerely believe it deserves to be right up there....(2 cents)