TOD: The first film I remember seeing that had "gay" anything referenced was, I think, "The Detective" with Frank Sinatra. Of course, in that film, "gay" was treated by others as "deserves to die" and by Sinatra's character as "sick creatures deserving pity", and possibly institutionalization.
I, too, recall "The Gay Deceivers" as probably the first gay-themed movie I saw.
After that came "Making Love", "Partners", "The Ritz," "The Boys in the Band", and "Victor, Victoria".
I also recall the Perry King-Meg Foster "A Different Story" that Dan (the Man) mentioned. I was confused by his comment about Foster being the 2nd actress to play Detective Lacey. Foster, of course, played the part on the TV series and was summarily replaced after six episodes by Sharon Gless because, "they say", they wanted someone "more feminine" in the role. I still scratch my head over that one because Gless was about as butch as they come in that part. I feel certain it was Foster's eyes that gave her a steely look that unsettled "the men folk" in charge and made them feel less-than-remotely-adequate that engendered the change.
I've seen only one play with a gay theme: "Jeffrey".