It depends on if you want a song with solos or or not.
If you want several featured soloists, "You Can't Stop The Beat" from Hairspray or "One Day More" from Les Miserables would be pretty good.
"Forget About The Boy" from Thoroughly Modern Millie works well with a female cast, but it's nothing without tap-dancing. "Madame Guillotine" from Scarlet Pimpernel is very different and quite chilling. If you just want singing and no dancing, "The Ballad of Sweeney Todd" might be an excellent choice.
Although I hate the musical "Starmites" in general, I quite like this song:
http://www.youtube.com/watch?v=oj905PsO2pk That's not my school, but I wish it was.
In my pants, she has burst like the music of angels, the light of the sun! --Marius Pantsmercy