What are a few major examples of symbolism in The Great Gatsby?

As a review, symbolism is objects, characters, and colors
that are used in literature to represent abstract ideas or
concepts.

F. Scott Fitzgerald loved using symbolism to
convey his feelings on human nature and the era in which he
lived.

Some of the major symbols and the meanings (that I
teach to  my students through my research) are
below:

Daisy's green light that Gatsby could see from his
house represents Gatsby's hopes and dreams specifically, and since Gatsby represents all
Americans, it also represents "The American Dream" of love, wealth and happiness for all
of us.

The Valley of Ashes (the desolate ash-dumping piece
of land) represents the moral decay of 20's and the plight of the
poor.

The billboard with the eyes of Dr. T.J. Eckleberg
represents the eyes of God looking down on the moral morass which was America in the
Jazz Age...and judging it badly.

The unopened, unread books
represent the shallowness of the rich who look good from the outside, but have no
content within themselves.

The owl-eyed man could be a
prophetic reference. Someone who is wise (the owl) and sees more clearly (glasses)  than
those around him what is happening to the society.

The
colors yellow and gold are used frequently, probably to represent wealth and money of
this society. White is used for Daisy often..presumably to represent her femininity and
innocence.