I will have to agree with kokomo that many of the tracks suggested are unsuited as reference material, due to excessive processing/post-production/lack of dynamics, etc.
The three tracks I suggested all have different properties relative to BeoLab playback. I've personally chosen to go with B&O's acoustic lens equipped speakers (BL5/BL3), as I believe they are unmatched when it comes to acoustic performances.
The first track is an "ancient" recording. On some speakers you get a musical experience, but the soundstage doesn't open up. There are more than 30 musicians on stage, and you should have a feel not only for them, but for the audience listening (and going wild) - with precise placement of the musical instruments. Compared to today's recording technology, this is low-fi, but B&O speakers give it life, trust me. Duke Ellington's Newport 1956
recording. Diminuendo in Blue, Live.
Hugh Masekela: Stimela (the version found on Hope). This is much used in hi-fi circles. Again a live performance, incredible instrumental contributions by the band, and then Masekela singing, playing the trumpet and speaking, with the live audience unable to prevent themselves from responding enthusiastically.
I have had people cry when hearing this in my listening room.
Elina Garanca: Werther, from her debut album. There may be edits here - but this is a sublime recording and performance, with bad speakers cracking up as Garanca tests their tweeters. The orchestra explores everything from tutti to sotto voce, and the ability of your speakers to provide details will be tested.
All three recordings have a large soundstage. Two of them have vocals, with a high degree of intimacy - one male and one female.
One classical recording - suffering slightly from Deutsche Grammophon's tendency to close-mike - but then a good set of speakers let you listen for that.
The Hugh Masekela recording must be heard to be believed -- you'll test your bass, your highs, your detailing, your soundstage, the depth illusion.
And Diminuendo in Blue has an interesting property. When I play that back in full resolution (CD), I can play it as loud as I want. When I play it back as loudly in iTunes Store resolution the tweeters on my BL5s go mad when Gonsalves hits the highs at the end of the track. Apart from that, another recording that will show off a pair of BeoLabs.
(I don't have much recent listening experience with the B&O speakers that do not have acoustic lenses.)