There have been a number of guides and websites to The Simpsons that provide lists of movie references and parodies. However, none of them are visually comprehensive. Coming close, though, are a few sites that place side by side a Simpsons still and its corresponding reference. Here, we can really see how dead-on some of those frames are, and how loosely adapted some others are. So, in preparation for the soon-to-be-released Simpsons Movie DVD, a blog titled The Adventures of Accordian Guy in the 21st Century (aka JoeyDevilla.com) put up a decent collection of these comparison shots over the weekend. He admits he found the images, but his spread is appreciated, nonetheless. He also doesn't list the movies, so I'll take a second and list the ones included: The Shining; Vertigo; The Graduate; Citizen Kane; Miracle on 34th Street; A Clockwork Orange; The Godfather, Part II; Goodfellas; Tom Jones; The Karate Kid; Psycho; Full Metal Jacket; The Longest Day; Apocalypse Now; Stripes; An Officer and a Gentleman; The Ten Commandments; North by Northwest and Saboteur. Additionally, the blog has posted small, individual sections on Simpsons tributes to Raiders of the Lost Ark; Citizen Kane; Midnight Express; It's a Wonderful Life; 2001: A Space Odyssey; The Pride of the Yankees; One Flew Over the Cuckoo's Nest; How the Grinch Stole Christmas and Steamboat Willie.
Obviously there are countless more movies the blog doesn't include (commenters mention some good ones), as well as a number of shots and references within his list that are excluded. But we must understand that a comprehensive project would take a long, long time. However, if you know Spanish (or even if you don't), you could take a look at Actualidad Simpson's movie reference section, which is apparently where the blog got the images (I couldn't tell you if they took them from elsewhere), and where there are lots, lots, lots more (with titles).