I remembered, having been distracted after the fact, that - despite a lengthy and technical (sort-of) piece on headphones - I did not list my reference tracks and works.
1. Gustav Mahler, Symphony no. 8, DSO-Berlin (Kent Nagano, DHM)
2. Richard Wagner, Das Rheingold, Staatsoper Stuttgart (Lothar Zagrosek, Naxos)
3. Wolfgang Amadeus Mozart, Piano sonata no. 11 in A, Mitsuko Uchida (Philips)
4. Elton John, "Postcards from Richard Nixon," The Captain and the Kid
5. Johann Sebastian Bach, Goldberg-Variationen, Pierre Hantaï (Mirare)
6. György Ligeti, Étude 13. L'escalier du diable: Presto legato ma leggiero, Aimard (Sony)
7. Robert Schumann. "Mit Myrthen und Rosen," Peter Schreier and Andras Schiff (Orfeo)
These tracks, even in 128 kbps AAC (I'm not sure about MP3), will do a pretty good job showing what your 'phones are capable of. I think there's a pretty good mix of vocal (both solo lyric, operatic, and choral), orchestral, and instrumental in there. The one pop song on the list, Elton John's strange and strangely addicting "Postcards from Richard Nixon," is pretty good for putting 'phones through their paces. Sir Elton has been crafting pop that earns the name, and - while he probably can't stand against Wagner, Mozart, Bach, and Mahler, his stuff is better than most popular music out there today.
For the record, the song my computer alarm plays every morning at 7:45 is "Postcards from Richard Nixon."
I would never ask you to do anything I wouldn't.