Another topic to consider is to what degree Antigone's being a woman has to do with her tragic end. Is it because she defies the law about women that Antigone meets her end, or is it because she defies Creon's edict? That is, what role gender plays in this tragedy could be a topic.
One theme might possibly be this: what makes this a great and powerful tragedy, as it is usually considered? More specifically, how is the work designed, structured, and written in such a way that it has an memorable impact? Of course, you will probably be reading a translation, and it is always difficult to judge the quality of literary works unless one can read them in the original language. However, you may be able to find a fairly literal translation (the ones in the Loeb Classical Library tend to be fairly literal) and can try to discuss what, exactly, makes this play a classic. Anyone could have written a play on the same topic; what literary qualities make this particular treatment of the topic powerful? One advantage of this topic is that you will have plenty to write about. Another advantage is that you will actually be discussing the play itself, not merely the ideas or "themes" the play contains.
Another thesis, along similar lines, might involve discussing how and to what degree this play fits Aristotle's definition of a successful tragedy.
I think an interesting topic in regards to this play is the question of "whose story is it, really?" The title of the play is Antigone, and it is clearly about her choice to bury her brother and defy Creon, but Creon is the character who survives the tragedy of the end, so is it ultimately his story? How does that fit into the tradition of Greek tragedy as defined by Aristotle?
Themes are always a great thing to examine when looking at any text. Given the wonderful themes present in the text (choice/consequence, custom/tradition, God/religion, and betrayal), any of the themes could be used to analyze Antigone.
Another great way to examine a text in an essay is through character analysis. Character analysis allows a reader to dissect a character and explain how they, as the reader, sees the character.
As you probably know, the most important part of a paper is a strong thesis. With a strong thesis your paper will flow much better. Let me offer a few possible topics.
First, you can ask if Creon is a tragic hero. You can look at the Poetics of Aristotle and determine whether he is a tragic hero. If you argue that he is a tragic hero, what are your reasons? These can be your supporting points. Keep in mind that in the end he does change his mind and decides to show clemency to Antigone. If you argue that he is not, why?
Second, you can ask what Antigone's tragic flaw was. In other words, was her hubris her unbending desire to bury the body of her brother or something else?
Third, another interesting question may be on the religion implications of the non-burial of Polynices. Perhaps, we can argue that this was a sacrilegious act on Creon's part. In this sense, the one with hubris would be Creon.
Finally, you can look at the work from a historical perspective. It was written after the Peloponnesian war. It was a time of sober reflection for the city of Athens. How does this show in the work?