If you are the kind of oddball who reads this blog, you should get to know Ubuweb, the website that collects large amounts of avant-garde art, in all possible forms. The site tends not to respect copyright, but gets away with it because it compiles material that has little commercial appeal.
A recurring feature of the site is the monthly top ten list, in which an artist or editor or critic or whatever is asked to list ten favorite items on the site. The June 2017 list, from Samuel Andreyev, selects modern classical music, one of my passions. His top ten list is a good survey of the classical avante-garde of the past few decades, covering 12-tone music (Webern), electronic music from Stockhausen, George Antheil, Morton Feldman, and other interesting sounds. I downloaded all 10 tracks and then put together a playlist on Google music. (Andreyev is a composer who has a YouTube channel devoted to classical avant-garde.)
I don't expect everyone to share my interests, but browsing the other top ten lists is a good entry point for the site. Here is my attempt at an Ubuweb top ten.
Ubuweb isn't a good place, however, for obtaining Robert Anton Wilson material. For that, I would suggest the Internet Archive.