Yep, take music you know well and have been listening to for years. You should hear detail, bass, texture etc you've never noticed before.
Having said that, when dem'oing recently I also used the following:
Massive Attack, Unfinished Sympathy - has 'hidden' low-end 'thunder' during intro, some speaker/amps reveal, some don't...
Cee Lo Green, Bright Lights, Bright City - good test of organisation/rythm, can sound a 'flubbery'/boomy mess.
David Bowie, Always Crashing In The Same Car - good test of mid-range detail and texture.
Frank Sinatra, Moon River - there're a few bars of guitar during the finale, if it's clearly audible, you've great detail.
Melody Gardot, Our Love Is Easy - if all of the above qualities are revealed and her voice has no sibilance, you've reached audio/musical nirvana.
And probably spent over £30k on perfectly matched speakers/amp/source