The only reason I suggested other musicals from that time period was because they are likely to be in a similar style. Just so you know, some well-known ones are Fiddler on the Roof, A Funny Thing Happened on the Way to the Forum, Mame, Jesus Christ Superstar, and Pippin. There is a wealth of audition material out there, search around on Wikipedia, youtube, musicals.net, musicaltheatreaudition.com, Yahoo! Answers.
Of course, you can pick a song from any musical. I would not recommend going with the suggestions above: anything from The Phantom of the Opera, Les Misérables or Wicked is way overdone (as are others, but those are the big 3), and Sondheim is notoriously difficult to play (not always, but as a general rule…)
I have two other suggestions:
‘Always True to You (In My Fashion)’ from Kiss Me, Kate
‘Raunchy’ from 110 in the Shade (technically a soprano role, I think, but look it up)