I think that the previous thoughts were well placed.  I would suggest that any title be strongly linked to your thesis statement.  Some of the most boring titles are actually the most informative because they are directly connected to the thesis statements that are present in the work.  In developing a title, I would ensure that the thesis statement is properly reflected.  Another option would be to use titles of songs or films that can connect in a humorous, yet informative manner, the ideas being brought out in the paper.  This can only really be done by the author of the paper who knows the subtleties of the writing.  I think that something like "Black Magic Man and Women:  The impact of the supernatural in Macbeth" might be an example of this.

Concerning your need for a title for your essay on ambition and prophecy in, I'm assuming, Shakespeare's Macbeth, no one can really suggest a title without reading the essay.  Writing a title for a literary essay, however, isn't as difficult as you may think.  Any title for a literary essay should include the following three things:

1. The author of the work you're studying
2. The title of the work you're studying
3. Something of your approach to the work

Thus, your title should be something as simple as:  Ambition and Prophecy in Shakespeare's Macbeth.  Your only concern is probably whether or not you want to be more specific than just using ambition and prophecy.  If you deal primarily with the character of Macbeth, for instance, then you might want to narrow down your approach to just that one character.  Or if you reach a specific conclusion from your study, you could include that in your title.  Of course, if you're looking for something particularly witty, you're on your own.  But even so, you still need to include the above three requirements.