I use well-recorded classical or jazz for system evaluation (as well as listening pleasure). I avoid electronic music for that purpose, as even though it might sound good, there is no guide to how it's really supposed to sound. Counterintuitve, as a do a weekly electronic music show for a college radio station...
+ 1 well recorded classical music example by Ricercars independent early music label.
New
in my collection 
A little late, but here I go. I like the opera. (not all of them, there are many unbearable works) Undoubtedly, Callas was the greatest female exponent, connoisseurs say that what made her stand out above all the others (and that includes those that came later, Anna Netrebko and others) is that in addition to his marvelous and in tune voice added a gesture that blended in its maximum expression with the lyrics. Judge for yourselves.