One approach to identifying the symbols of Lord of the Flies is to consider William Golding's novel a religious and psychological allegory.  By doing so, the characters can represent, or symbolize, certain types.

As previously mentioned, the island is like the Garden of Eden on which the boys arrive from a society engaged in war.  Now that they are removed from the war and the influence of society in the form of adults, the boys must survive by using their own natural inclinations and thoughts.  Each of the main characters, then, represents--symbolizes--a certain type of person. 

• Ralph, is the golden boy, the born leader type.  He is symbolic of the physical presence for leadership, a charismatic type, as it were.  At the same time, he is symbolic of the innocent, the ingenuous, who is unprepared for dealing with "the evil that men do," as Shakespeare wrote in Julius Caesar.
• Piggy is the intellectual, the voice of reason without the brawn necessary to deal with savage forces. His heaviness, near-sightedness, and thinning hair connote age and its acquired wisdom.
• Simon is the intuitive type.  He learns through emotional, rather than intellectual, experience as does Piggy. Because he feels, rather than rationalizes, knowledge, it is impossible for him to verbalize his realization that the evil on the island is intrinsic to the boys and not a "beast."
• Jack symbolizes the penchant for savagery and the intrinsic evil in man.   Roger best explains this intrinsic evil as in Chapter Four he restrains himself from striking Henry with the stones--"that token of preposterous time"--he throws only because the "taboo of the old life"/his conditioning "by a civilization that knew nothing of him and was in ruins." 
• the pig's head is Beelezebub, the devil.  It represents the evil in man after his fall and expulsion from the Garden of Eden.
• the conch is symbolic of order.  Like a gavel, it is meant to call the boys to order.  However, once anarchy takes over, the conch loses its significance and is broken against the ancient stones.

In my opinion, the major conflict in this novel is the conflict between people's "good" and "civilized" instincts on the one hand and their "bad" and "uncivilized" instincts on the other.

I would say that Ralph and Jack symbolize this conflict.  Ralph symbolizes the good and Jack symbolizes the bad.

The conch, of course, is a symbol of civilization as well.  That is because it is used as a way to try to civilize the boys -- it is used to call them to meetings and it is used to make sure that they do not talk out of turn.

I'd say that Piggy and his glasses symbolize intellectuals and science and how they are used by society.

Simon represents morality and is seen by some as a Jesus figure.