The Green Light and the Color Green
The green light at the end of Daisy's dock is the symbol of Gatsby's hopes and dreams. It represents everything that haunts and beckons Gatsby: the physical and emotional distance between him and Daisy, the gap between the past and the present, the promises of the future, and the powerful lure of that other green stuff he craves—money. In fact, the color green pops up everywhere in The Great Gatsby. Long Island sound is "green"; George Wilson's haggard tired face is "green" in the sunlight; Michaelis describes the car that kills Myrtle Wilson as "light green" (though it's yellow); Gatsby's perfect lawn is green; and the New World that Nick imagines Dutch explorers first stumbling upon is a "fresh, green breast." The symbolism of green throughout the novel is as variable and contradictory as the many definitions of "green" and the many uses of money—"new," "natural," "innocent," "naive," and "uncorrupted"; but also "rotten," "gullible," "nauseous," and "sickly."
The Eyes of Doctor T. J. Eckleburg
The eyes of Doctor T. J. Eckleburg on the billboard overlooking the Valley of Ashes represent many things at once: to Nick they seem to symbolize the haunting waste of the past, which lingers on though it is irretrievably vanished, much like Dr. Eckleburg's medical practice. The eyes can also be linked to Gatsby, whose own eyes, once described as "vacant," often stare out, blankly keeping "vigil" (a word Fitzgerald applies to both Dr. Eckleburg's eyes and Gatsby's) over Long Island sound and the green light. To George Wilson, Dr. Eckleburg's eyes are the eyes of God, which he says see everything.
The Valley of Ashes
An area halfway between New York City and West Egg, the Valley of Ashes is an industrial wasteland covered in ash and soot. If New York City represents all the "mystery and beauty in the world," and West Egg represents the people who have gotten rich off the roaring economy of the Roaring Twenties, the Valley of Ashes stands for the dismal ruin of the people caught in between.
East and West
Nick describes the novel as a book about Westerners, a "story of the West." Tom, Daisy, Jordan, Gatsby, and Nick all hail from places other than the East. The romanticized American idea of going West to seek and make one's fortune on the frontier turned on its ear in the 1920's stock boom; now those seeking their fortune headed back East to cash in. But while Gatsby suggests there was a kind of honor in the hard work of making a fortune and building a life on the frontier, the quest for money in the East is nothing more than that: a hollow quest for money. The split between the eastern and western regions of the United States is mirrored in Gatsby by the divide between East Egg and West Egg: once again the West is the frontier of people making their fortunes, but these "Westerners" are as hollow and corrupt inside as the "Easterners."
Gatsby's mansion symbolizes two broader themes of the novel. First, it represents the grandness and emptiness of the 1920s boom: Gatsby justifies living in it all alone by filling the house weekly with "celebrated people." Second, the house is the physical symbol of Gatsby's love for Daisy. Gatsby used his "new money" to create a place that he thought rivaled the houses of the "old money" that had taken her away.