Sogood51...Try ANY of the Tacet Chamber music DVD-A's available from elusivedisc.com.
It's hard to choose among them, but the Mozart Flute Quartets DVD D107 is I think the best example of multichannel recording. This one shows you why you need good speakers in the rear.
The Schubert "Trout" Quintet DVD 106 is a good performance of a favorite work.
For a change of pace, try The BlueGrass Sessions, Tales From the Acoustic Planet Volume 2...Bela Fleck..Warner Bros.
This is a jam session in your living room.
For an orchestral work, try Mozart Piano Concerto, MDG 940 0967-5 (again from elusivedisc). This one is mastered in 2+2+2 speaker configuration which is way better for audio than the 5.1 configuration designed for movies. It sounds good in 5.1 playback mode, but you might want to rig up the 2+2+2 arangement as an experiment. By the way, this 2+2+2 setup and others which incorporate a "height" speaker demonstrate the flexibility of the DVD-A protocol (in comparison with SACD). The video display of the program, and ability to select tracks from the on-screen display is neat too.