I prefer the examples to be from films, but books are all right,too.
I cannot use a lot from stories found in college level LIT classes.
I agree that Star Wars is a useful film for this purpose. However, almost any dystopia will also work. I can think of The Island and The Truman Show, as well as I Robot as allegorical films. Also use film versions of Fahrenheit 451 and 1984.
You can also include the Star Wars mega-epic series of films, as #5 correctly suggests. They have a clear good side and a clear bad side with very little shady ground and therefore could be said to be allegorical in terms of the battle between good and evil. Lord of the Rings is another excellent example though - it is really good to try and examine films as texts with their own literary devices. One of my favourite films for this is The Piano, directed by Jane Campion, which includes lots of sex but is very rich in symbolic overtones.
I'm about to suggest a movie I've never seen in its entirety, though I tried. Literally everyone who knows me thought I would just love it because it was so symbolic and (according to them) "literary," but I just couldn't get past the first 20 minutes. The Matrixseries is apparently allegorical, starting with the main character, Neo (meaning new, of course).
Also in terms of allegory you might consider the Lord of the Rings Trilogy, movies which are also filled with imagery and certainly symbolism. Any move with clear cut "good guys" and "bad guys" is probably some kind of allegory about good and evil, and often there are obvious uses of symbolism along the way (as is true of the ring in Lord of the Rings).
One of the films that I saw recently that sticks with me is the film adaptation of All Quiet on the Western Front. There have been two films made to date, but the first one from 1930 directed by Lewis Milestone has excellent images that show the nature of war. The film is obviously in black and white, and there is a scene when the protagonist Paul falls into a shell hole and is stranded there as the battle wages. The image of soldiers jumping over the hole in pursuit of the enemy and then the fading in and out of the scene gives a realistic quality to the image being portrayed.
Animal Farm is another great choice, and I don't think this book is often used in college literature courses since it is used so much on the high school level.
Animal Farm in itself is an allegory. It represents the ideal, Utopian animal society, and it is also a functioning farm. Each animal on the farm also represents himself as a character and something bigger than just that character.
The ribbons in Molly's hair are symbolic of the human attention she is used to getting and craves. On Animal Farm, she no longer had these ribbons or the petting, pampering life she had under the care of the humans. Consequently, she ran away and is spotted by the animals later in the company of a man who has put brand new blue ribbons in her mane. Of course, there are many other symbols in the book/movie.
Connotation is evident as well in the very way the rules were changed to suit the ruling government. The wording changed in this one example from "no animal shall kill another animal" to "no animal shall kill another animal without cause" to cover the Pigs brutal slaughter of those animals who stood up to them.
Imagery is simply a picture created with the words the author has chosen. You would probably have to read a screenplay to get this from film since everything is so visual in this medium. However, by reading a screenplay, you get the idea of the scene the author has in mind.
One novel with a movie based upon it that might work well in illustrating symbolism and imagery is Joseph Conrad's Heart of Darkness and the film Apocalyse Now. For instance, as Marlow journeys down the river in order to find Marlowe, he encounters fog which represents his clouded thinking and confusion; that is, his indecisiveness regarding Kurtz, as well as his own existential questions. Also, the savages may also be perceived as symbolic, for their attack parallels Marlowe's internal struggle. Of course, the impaled heads on sticks near Kurtz symbolize his descent into utter evil and savagery and alienation.
The painting by Kurtz that hangs on the wall of the brickmaker's house is, of course, symbolic of the failure of the white colonists as the painting shows a blind-folded woman holding a torch in her hand. The torch represents the light of civilization while the blind-folded woman represents the colonists who have lost their inner-sight.
Another example is Herman Melville's great metaphysical novel, Moby Dick, which is replete with symbolism. The chapter (36--"The Quarter Deck") in which Ahab has a communion service with the harpoonists drinking from the uncapped ending of their harpoons is significant. And, of course the chapter (42) on the whiteness of the whale discusses the symbolism of white as an evil color in many things.
I am not sure why you would need them from films, but if you find any classic film on literature, you will find much valuable information for your assignment. Try watching any film version of Vanity Fair, and you should have more than enough for your paper.