Monitoring is done during recording, mixing and mastering. Sorry to get technical on you, don't mean to confuse you, so OK, they are used for recording.
What I have on my test CD are:
1. Pink Floyd: Marooned - 3D imaging, holography and drum impact
2. Coldplay: Don't Panic - Bass, baby, Yeah!
3&4. Mark Knopfler: Back to Tupelo, Shangri-La: Lower midrange clarity and separation of voice/guitar
5. Diana Krall: A case of you - Micro-detailing, lots of audience noise in this quiet live piece
6. Richie Sambora: Ava's eyes - Micro detailing (breathing, finger noise), tone
7. Sarah Maclachlan: Full of Grace - Upper midrange and female vocal clarity, no sibilance
8. Van Morrison: Moondance - OK recording, but good check of 'groove', very fast bassline, should have no 'overhang' or 'boom'
9. Dire Straits: Why worry - I use this as it's actually got a very poor drum recording in the end of the track. Reality check - it needs to sound bad, then the system is faithful.
10. Coldplay - Fix you. This is one hell of a noisy track. A system should not lose its composure or get painful towards the end o the track, when all hell is breaking loose.
There are a few other songs on that disc I don't remember off the top of my hat.
Other songs that I've figured out are good are:
1. Pink Panther (Really!)
2. Hamp and Getz: Headache
3. AC/DC: Back in black
4. Zucchero and Tina Arena: I'm in trouble
5. Oasis: Champagne supernova (this is a tricky test, the bass is actually very low down and most systems just repoduce the distortion, not the original tone)
6. James Taylor: Gaia. If a system can reproduce the drum roll after the bridge without bottoming out at your threshold of pain, then it's worthwile to buy)
7. The Eagles: Hotel California, the regular version (I can't stand the unplugged version anymore anyway), for just the impact of tom rolls before the final verse ends, and at the crescendo of the chorus. And yeah, there are six guitars in the song, each at a different position. On a good system you can pinpoint all six.
8. Dire Straits: Love over Gold, Private investigations
9. Paul Simon: Diamonds on the soles of her shoes
10. Bruce Springsteen: Paradise, Nothing man, Blood Brothers
I also carry a bit of jazz and fusion, but dealers normally stock quite a bit of that sort of thing themselves.