The Avant Garde Project has a large collection of free music that you can download, including digitized LPs of long out-of-print electronic music works:

The Avant Garde Project is a series of recordings of 20th-century classical-experimental-electroacoustic music digitized from LPs whose music has in most cases never been released on CD, and so is effectively inaccessible to the vast majority of music listeners today.

The analog rig used to extract the sound from the grooves is near state-of-the-art, producing almost none of the tracking distortion or surface noise normally associated with LPs.

New AGP installments are released as bittorrents each Friday night around midnight (GMT), and can be accessed through either The Pirate Bay or Mininova. New torrents are announced on the I Hate Music Forum.

The AGP archive is a repository for earlier installments, the files of which can be downloaded from this website.

You can preview an example track, Morton Subotnick’s A Fluttering of Wings, below.

It comes from the sixth AGP installment, which contains Morton Subotnick’s series The Double Life of Amphibians. This series includes four of the fourteen works that Subotnick wrote for “ghost” electronics in the late 1970s and early 1980s.

The “ghost” electronics make no sound on their own, but alter the amplitude, frequency, and location of any sounds produced as the electronic score is playing. In his works for this technology, Subotnick explored the effects of these manipulations on a variety of instrumental combinations, from single instruments to chamber ensembles. The rather simple electronic manipulations in the “ghost” electronics nevertheless produce an interesting range of timbres, depending on the tone color of the instruments being manipulated.

While Subotnick is known chiefly as a composer for electronics, his instrumental writing in these works is interesting and innovative even in those passages where the electronic manipulation is minimal.