The Other Minds catalog of recordings housed at the Internet Archive (aka archive.org) contains decades of recordings, an ongoing history of 20th- (and, now, 21st-) century classical music. And it’s updated regularly.
Perhaps setting its own record for the shortest period from performance to broadcast, just two days ago it posted the live performance from November 2, 2007, of Italian vocalist Amelia Cuni , who is trained in traditional Indian dhrupad singing, and a trio of musicians — percussionists Raymond Kaczynski and Federico Sansei, and Werner Durand on a variety of electronics — performing John Cage‘s 18 Microtonal Ragas. This is the same concert that I attended and later wrote about back on November 17 (disquiet.com). The piece is available as four MP3s (MP3, MP3, MP3, MP3). More info at archive.org.