You need something that really shows how great and versatile your voice is, heres a few ideas of cool sing songs:
-Vannessa Carlton - A thousand miles, classic, everyones heard it.
-Beyonce - Listen, Powerful, up for a challenge?
-Lady Gaga - Paparazzi (this one is very good, it has high parts in the chorus, theres a great contrast between the chorus and the verse, the verse is quite choppy and hard, whereas the chorus is very strong and emotional, I did this for a show once, it went down very well, and I'm no Whitney either :P)
-Christina Perri - Jar of hearts, very emotional, I can imagine with alot of practice it could be really awesome.
-Christina Aguilera - Beautiful, also everyone knows this one, its risky, but could be very impressive.
Can't think of any others at the moment. But hope you find a good song for you, and hope the audition goes well :)
Choosing songs for performances of mine :P