Much of the symbolism in Antigone lies in the characters themselves. Antigone and Creon represent a number of opposing forces: male vs. female, family ties vs. civic duty, man vs. nature, and man's laws vs. the laws of the gods. Also, there's the blind prophet Teiresias who could be seen as representing the will of the gods. Check out the "Character Analysis" section for more details on the larger symbolism of the characters.
Images of tombs and burials pop up a lot in the Oedipus plays. In Antigone, Creon causes all kinds of problems by bungling issues of burial. The prideful king has committed a double blasphemy by letting Polyneices's body go unburied, while entombing Antigone when she's still alive. At points we feel like saying, "No, no, Creon. It's the dead ones that go in the ground." The symbolic paradox of Creon's double blasphemy, shows just how far from sensible Creon's hubris has taken him.
Also, Antigone's fearless march to her own entombment and talk of being a bride to death suggests that she feels closer to her dead family members than to the living. She seems to have no problem at all leaving behind her sister Ismene and her fiancé Haemon, but talks of how swell it will be to reunite with Oedipus and her brothers in death. When Antigone takes her own life inside her tomb, it could be seen as symbolic of the fact that she's found the tragic fate she always knew awaited her.
There's tons of bird imagery throughout Antigone. For one, there's lots of talk of carrion birds making a buffet of Polyneices. The Chorus also describes Polyneices himself as a bird, a big mean eagle wreaking havoc on Thebes. This description seems to heighten the idea of Polyneices as fearful aggressor against his home town. The Chorus even goes so far as to describe Polyneices the eagle as feasting on their blood. This becomes pretty ironic when the birds are feasting on him.
Another instance of avian imagery is when the Sentry describes Antigone as hovering over Poyneices's body like a mother bird. Here the bird reference seems to strengthen Antigone's symbolism as both a maternal figure as well as representative of the ancient force of nature.
The biggest bit of bird symbolism comes from Teiresias. This is not a surprise, since the prophet is skilled in the magic art of augury or telling the future from the behavior of birds. The seer tells King Creon all about how the birds are fighting each other, which symbolizes the horrible imbalance the King has created in nature. Teiresias goes on to tell Creon that the birds won't talk about the future because they've gorged themselves on Polyneices's blood. (Yuck.) The birds have evidently also pooped all over the altars of Thebes. (A bad day for the altar cleaner.) All this foul bird imagery (pun intended!) seems to symbolize the corruption that Creon has caused by not burying Polyneices.