"Down to the River to Pray" off the Oh Brother soundtrack is one of my favorite test tracks. Very relieving of system differences. I always take it to audio shows and meets.
The sound of the choir, the room and how Alison fits into the mix can be rather different on different systems. Some don't get the slow crescendo at all, and every system changes the sound of the room the choir is in.

Lot's of other good stuff on the CD too.