My other favorite expressionistic opera: Bartok's Bluebeard's Castle. This is a little less weird, and more tonal than Schoenberg, but it is still out there.

16/44 FLAC Download
I'm surprised by how many recordings there are of this piece, but two of the first are still the best. YMMV. This one by Kertez on London and Dorati on Mercury. Both have great playing, great singing and great sound.