I am listening to "Festival", a John Atkinson recording under the Stereophile Magazine disc series.
It is Aaron Copeland (amazing US composer) recorded with B&K 4006s.
Beautiful recording, great soundstage, not a shabby test recording, but for the low background noise from either air-handlers or older dithering method. It has recently joined my short list of favorite test CDs.
I like Buena Vista Social Club, Pink Floyd's DSOTM, Steely Dan's Aja, and, of course, a few of my own pulls which include Bela Fleck, some acoustic string stuff, and SCI.
There was a thread for a TS reference disc, but I don't know if it ever bore fruit.