Apparently repeating "I see a little silhouetto of a man" to Siri will get her singing Queen's iconic 'Bohemian Rhapsody'. It's supposed to work on any device with Siri. I just tried it on my phone but it didn't work because my phone is a cordless house phone. My mom did yell at me to hang up though because she was talking to her sister in Florida.
Keep going for a video demonstration using an iTouch smartpad or whatever.
Thanks to Luc, who agrees Siri should learn more songs and start her own band.