Cult movies? This also varies from generation to generation and depends on whom makes the reference and what his criteria would be. However, the most typical and undeniable iconic example of a Cult Classic will be The Rocky Horror Picture Show.
Epic Movies? Even though the genre has existed since the early 20th century the definition of what it exactly is tends to differ from viewer to viewer. Usually the term is used for movies about some great adventure that usually take more than two hours in length or will need a few sequels to tell everything. Star Wars and Lord of the Rings are the most typical examples.
Porn movies? Deep Throat, Debbie Does Dallas. They tend to get confused with erotic movies, though.
Porn actors? Linda Lovelace, John Holmes, Traci Lords, Jenna Jameson and Ron Jeremy. At all other times references to specific pornographic films will typically be limited to Parallel Porn Titles (whether real or fictional).
War movies? Typically only set during the American Civil War and World War II for some tales of glory and heroism. If set during World War One and/or the Vietnam War it will usually be more War Is Hell.
Jim Carrey: It's rather sad that he is still most associated with making silly faces and the three films from the beginning of his career: The Mask, Ace Ventura and Dumb and Dumber, despite having tried to act in more serious films ever since.
Laurel and Hardy: Hardy will fall, bump his head, get something on his head, while Laurel looks and watches bewildered, scratching his hair. Expect one scene where Laurel pokes Hardy in the eye and Hardy looking straight in the camera with an exasperated look.
Harold Lloyd: Nowadays he is mostly remembered for one image from one film he made: Safety Last!, in which he is hanging on to a large clock on top of a skyscraper.
Bela Lugosi: Will be portrayed as Dracula, even though he only played the part twice.
The Marx Brothers: Groucho will wisecrack and insult Margaret Dumont, Chico plays piano and Harpo plays harp, after that chases women with a cow horn and all of them evoke complete mayhem. Also note that Zeppo is often forgotten or ommitted.
Monty Python: Whenever the name of this comedy group is dropped people will instantly begin quoting scenes from Monty Python and the Holy Grail, as if this is the only (good) thing the group ever did. Often you'll encounter so-called fans of Monty Python who actually just mean they like Holy Grail and are even totally unaware that the group also made other films and even had a TV series. Some of them even think Monty Python was a person! Usually John Cleese is the only foremost member everybody can name, except when you're a Python fan, of course.
The Three Stooges: Will poke each other in the eye, hit each other on the head and the following lines should be mentioned: "Soitenly", "I was a victim of soicumstance", "Wiseguy, huh?", "Woob Woob Woob", "Yuk Yuk Yuk".
Michael Bay: Makes only special effects blockbusters. Point of reference is Transformers: a franchise everybody hates, yet all go and watch every time a new installment is made, just to bitch about it on Internet forums afterwards.
Sergio Leone: Only directed spaghetti westerns in the popular consciousness.
George Lucas: All he ever did was make Star Wars and while fans adore the franchise in almost religious fashion he is nowadays hated for singlehandedly destroying everything what was great about it in the first place.
Michael Moore: Makes sensational left-wing documentaries that criticize everything right-wing people like, which explains why he is a polarizing figure. The only points of reference are Bowling for Columbine and Fahrenheit Nine Eleven. Typically most people who criticize Moore have only seen one or none of his movies and base their satire or criticism more on the fact that he is obese than anything else.
Oliver Stone: Makes left-wing conspiracy theory heavy movies about the Sixties and Seventies or that criticize the American government, capitalism and/or the army.
Quentin Tarantino: Still mostly associated with Pulp Fiction and blood splattering violence, even though this aspect only takes up a small part of his movies and usually happens off screen and/or in a comic book fashion hard to take seriously.
Paul Verhoeven: Typically people refer more to his Hollywood movies than the ones made in the Netherlands. Most refer to him as someone who just makes action packed violent movies and/or saucy erotic films, typically not looking much deeper into it.
Orson Welles: Citizen Kane seems to be the only film he ever made in popular culture. All other references are about his voice and/or his weight. Or the fact that he made some TV commercials later in life.
Usually the movies where the country itself is very visible in the background.
American movies? Before the 1970s all American movies seemed to be either Glamour or Western. After that date they have become synonymous with big spectacle blockbuster movies with a lot of gratuitous bullet rains, explosions and badass lines.
95% of James Bond parodies are a parody of the Sean Connery era films. The remaining 5%, at least nowadays, are the Bonds of the nineties and two-thousands; Pierce Brosnan or Daniel Craig. Roger Moore, George Lazenby, and Timothy Dalton? Who are they? (If you grew up at any time between 1975 and 1995, feel free to mentally delete Roger Moore from the above list. He was undoubtedly the most successful James Bond of the late Cold War years.) The one-film Lazenby is ALWAYS mentioned whenever someone wants to sound extremely knowledgeable about the Bond Franchise.
All teen comedies were by John Hughes. (Amy Heckerling might get a mention if the reference is a little more "indie.")
Speaking of that, you would have a hard time finding a casual John Hughes fan who could remember any members of his repertory of teen actors other than Molly Ringwald, Anthony Michael Hall, Ally Sheedy, Emilio Estevez, Judd Nelson, Jon Cryer, or Andrew McCarthy, even though there were many, many more. (And no, knowing the name of a character, such as "Long Duk Dong," doesn't count; the person has to know the name of the actor.) And that doesn't even include young actors who became famous outside of Hughes's works, and are associated with him only due to Retroactive Recognition (Robert Downey, Jr., for example). Lampshaded by the 1997 book Pretty in Pink (about 1980s teen movies), which ended with an appendix listing many of the unsung Brat Packers that was wittily titled "Don't You Forget About Me."
Notable exceptions of this trope from films and this trope Played With in film:
Quentin Tarantino's movies are full of shout outs and homage shots to movies most people do not even know exist, such as Goke, Body Snatcher From Hell, where he got the idea for the red background during the flight scene in Kill Bill Vol. 1.
The indie film Little Miss Sunshine features a Proust scholar as a main character. He talks about Proust during an important character moment.
Parodied in the 1965 film version of The Loved One, in which Dennis Barlow romances Aimee Thanatogenous by quoting classic poetry to her and claiming it to be his own work.
In The Great Muppet Caper, Animal is described as being upset that he missed the Rembrandt exhibit at the National Gallery. Animal corrects him; "Renoir."
A rare humorous moment in Se7en, when Brad Pitt's character has never heard of the Marquis de Sade, and mispronounces his name "Shah-day", like the Nigerian singer Sade.
Lampshaded in Dogma with an appearance by the Metatron, the angel who speaks for God to humans who would be destroyed by the power of God's voice. The heroine attempts to make up for not knowing who he is by mentioning the Ten Plagues, to which the Metatron remarks "You people! If it's not in a Charlton Heston movie, it's not worth knowing, is it?"