If you have any sort of interest in avant garde music, then you owe it to yourself to check out The Avant Garde Project, a treasure trove of recordings of "20th-century classical-experimental-eloctroacoustic music"; all free and available as mp3s or lovely lossless FLAC files. In this ever-expanding archive, you'll find work by such luminaries as Morton Subotnick, John Cage, Harry Partch, Pierre Henry and Pauline Oliveros, and in a move that should keep them safe from the ire of the industry, they've restricted the repertoire to recordings that are out of print.
In addition to works by notable and less well known composers, the collection is rounded out with what the Project calls "found" avant garde music. Included under this loose rubric are an LP of haunting whale songs and an assortment of music boxes, street organs and mechanical musical instruments. (The explanation of the inclusion of the latter set of recordings is that they "arguably represent the origins of concrete music, in which the human performer is taken out of the equation".)
Whale Songs - Orca
Mechanical Musical Instruments - Track 4