What are some of the major symbols in The Great Gatsby?I've already noted the colors, green, yellow, and gold, the green light, and the weather...

Symbols abound in The Great Gatsby, depending on what kind of symbolism you're looking for and how deeply you want to go into it.  

The color symbolism, as you've already found, is pretty rich, but not always immediately noticeable. For example, the whole "egg" aspect of the Long Island neighborhoods, along with Daisy's name, both refer to things that are white (pure) on the outside, and yellow (corrupt) within. In another instance, Myrtle allows several taxis to pass by, waiting to pick a "lavender-colored one," symbolizing her desire to be perceived as a member of a higher, more "royal" class than the one she occupies.

Physical items can also be seen as highly symbolic. The billboard featuring Doctor T.J. Eckleburg's eyes loom over the "valley of ashes," and they can be seen as the eyes of God watching in passive judgment over a wasteland of poverty and corruption.

When he first reunites with Daisy, Gatsby is "reclining against the mantelpiece," until the clock "tilt[s] dangerously ... whereupon he turned and [catches] it with trebling fingers."  Given Gatsby's preoccupation with time and his desire to have Daisy and Tom's five-year marriage "wiped out forever," it's symbolic that he literally holds time in his hands after nearly toppling it. Additionally, during the fateful afternoon at the Plaza Hotel, the "portentous chords of Mendelssohn's Wedding March" waft from a ballroom, ironically symbolizing a marriage beginning, just as Daisy's and Tom's is being challenged. 

The names of the guests who attend Gatsby's parties that Nick compiles at the beginning of chapter four are symbolic as well; names like "Fishguard," " Hammerhead," "Beluga,"  "Civet," "Catlip," "Ferret," "Duckweed," and "Bull," all share associations with animals, symbolizing the recklessness and animalistic behavior so characteristic of Gatsby's uninvited visitors.

Finally, Gatsby's shirt collection that Daisy finds so emotionally captivating holds symbolic significance as well. They are "coral and apple green and lavender and faint orange," all pastel shades, that, like his "pink suit," symbolize Gatsby's carefree and romantic personality, as well as his desire to add to the "colossal vitality of his illusion" of himself.