Music to test with:

I have found myself coming back to same of the same recordings when I buy/audition a new piece of equipment.
I really like Jennifer Warnes "Famous Blue Raincoat" The Cowboy Junkies "Trinity Sessions" both of those on CD and LP. The Bangles "Eternal Flame" Bob James "Touchdown" Al Jarreaus "Mornin'" and even the Carpenters "Make believe it's your First Time" I have also used Andrew Litton conducting Tchaikovskis 6th symphony.
There are many more recodings I like but I was wondering what you use when you are auditioning something new?