spires and scrolled balconies in the heavily lightsome style of the seventies, set on what had once been our most select street. But garages and cotton gins had encroached and obliterated even the august names of that neighborhood; only MissEmily's house was left, lifting its stubborn and coquettish decay above the cotton wagons and the gasoline pumps-an eyesore among eyesores.

The Grierson house serves as a symbol of the dying Old South: Like the South in the days before the terrible Confederate defeat at Gettysburg, the house was once a proud example of fine architecture that had slowly eroded as the modern world surrounded it.

Homer Barron, the Yankee visitor, is a symbol of the new Northern encroachment upon the South--a modern day carpetbagger or scalawag who moves to the area for financial gain, meddles with the social establishment, then moves on to enjoy his profits elsewhere. Unlike the original carpetbaggers who plagued the South during Reconstruction, however, Homer was well-liked and popular with the townspeople, though his time was to be limited in Jefferson.

Emily's servant, Tobe, is also an obvious symbol of the last remnants of slavery. He remains with Emily until her death, and only then is his servitude finalized. When Emily dies, Tobe gains his freedom. 

Miss Emily's old, sprawling house is a symbolic reminder of the Old South and its traditions, and it is also a constant reminder of the father who guarded the house against suitors for his daughter.  It is a symbol to Miss Emily and to the townspeople of the past illustriousness of the family, and, ironically, of how far the family has fallen.

The watch that Miss Emily wears on a chain around her neck is symbolic of the passage of time and of Emily's impending death.  It also symbolizes the passage of time between generations, from the old Southern genteel society of which she was an active part to the new Southern society that has embraced more modern notions about women (and taxes, for that matter).

Lastly, the arsenic with which she poisons Homer Barron is a symbol of purging, of getting rid of that which poisons her.  Faulkner implies that Homer is "a rat" by having Miss Emily poison him with arsenic, when there are myriads of other ways she could have gotten rid of him.

You could also discuss the gray hair, the unfinished sidewalk, and, of course, the rose.