CROSS-DRESSING
In spite of all the furor about transgender people, allow me a little political incorrectness. I just think a man dressing up like a woman is somehow innately funny. In none of these films does the man actually convince us he really looks like a woman, but that’s part of the fun- we are in on the joke and the other actors are not. 
Absolutely no one in the world would believe Jack Lemmon and Tony Curtis in drag are women, but that doesn’t stop Some Like It Hot (1959) from being one of the funniest movies ever made. This is director Billy Wilder at the top of his game. Throw in a luscious Marilyn Monroe and Joe E. Brown as a millionaire smitten with the tarted-up Lemmon and it is a merry mess. 
Dustin Hoffman has stretched plenty in his distinguished career, but never further than in Tootsie (1982). Unable to land an acting job as himself, Hoffman dresses as a woman and finds jobs aplenty. He also finds himself to be a better person! A very sharp screenplay makes this a splendid film, and Hoffman is perhaps the most convincing of all the cross-dressing men in the movies. 
We do not for a moment believe that Robin Williams’ wife and children would not recognize him dressed as a woman in Mrs. Doubtfire (1993), but this being a movie, they do not. When he’s divorced and can’t live without being near his children, Williams dons female attire and hires on as the kids’ nanny. Hijinks follow. 
The very idea of the urbane Cary Grant dressed up as a woman is both ludicrous and funny, and is both in I Was A Male War Bride (1949). At the end of an extremely convoluted plot, Grant has to pass as a woman in order to get back to America. And it’s much fun getting to and beyond that point. 
The World According To Garp (1982), based on John Irving’s marvelous book features two separate men-in-drag sequences. John Lithgow was nominated for a supporting actor Oscar for his role as Roberta, “the old tight end”. And Robin Williams (playing the title role) visits a women’s rights rally in drag. This is a pretty good movie but nowhere near as good as the book (surprise!). 
I’m throwing in the Australian Priscilla, Queen Of The Desert (1994) with Hugo Weaving, Guy Pearce and Terrence Stamp as unlikely drag queens because it was a huge hit and was also made into a Broadway musical. But I didn’t much like it. 
It’s interesting that the only movies I can think of where the tables are turned and women dress up like men are miles from being comedies. In Yentl (1983) Barbra Streisand dresses as a male in order to get a good education. And in Boys Don’t Cry (1999) Hillary Swank dresses as a boy to pass in the street culture she chooses. Frankly, the charm of this movie eludes me, but it was hugely popular and Ms. Swank won an Oscar. There’s also Albert Nobbs (2011) with Glenn Close very convincing as a woman pretending to be a man so she can get a good job. Not funny!
All of the movies in this article are available on  DVD. The first four are ok for all ages; the last five are for mature audiences only.