Rules Of The Game (1939): Bunch of rich people go to a country estate in France for the weekend, love triangles become rectangles & every other shape in Jean Renoir's greatest film. Screenplay satirises an entire class of people, actors give life to said caricatures. Jean Renoir (son of Philippe Auguste) is excellent as Octave & as Director.
His Girl Friday (1940): Rapid-fire screwball comedy with Cary Grant & Rosalind Russell.
I personally prefer Holy Grail over Life of Brian since Holy Grail manages to never stop making jokes, from the opening credits to the abrupt ending. But I can see why Life of Brian receives more critical praise. For a start, it has more depth. And there are many great routines.
Duck Soup is fantastic, although A Night at the Opera is a close runner-up.
The first series of Blackadder is my favourite, and you left it out! I love having Baldrick as a schemer, Peter Cook as Richard III and Brian Blessed as Richard IV. I love the villains: 'The Thrush', 'The Witchsmeller', the six most evil men in the land. It's beautifully shot. It's also a fun bit of alternative history, and since I watched it first, a part of me long wished the other series also had more of an alternative history element to them.