I own some extremely bizarre underground stuff I collected during my touring/gigging days. Mostly demos of punk/artsy/industrial/fusion/WTF/etc type craziness from opening acts or just weirdos in the crowd handing me stuff. Lots of handmade DIY weirdness (I swear to god I have a demo from this one band where the totally weird ass chick lead singer told me they ran out of jewel cases so she cut pocket off her stinky, tour stained corduroy pants... like the whole pocket so her ass was showing, safety pinned one of their patches on it and stuffed the disc inside... and it is WEIRD music).
But I have to say the weirdest album by a well known artist I have is a cassette of Alice Cooper Live at the Whisky A Go Go from 1969. There are some tunes off the earliest albums but much of it is total WTF territory and they were obviously BLASTED out of their minds. Oddly enough I found it in the discount bin at a dollar store I was working at at the time (I was like 16 or something) amongst the Kenny G and "Solid Gold 50's" type crud. I listened to that thing endlessly and honestly I think it had a profound influence on my songwriting. It's all completely out of tune and off time and god only knows what the hell was going on on stage or in the audience (apparently that weird group of chicks that used to follow Zappa around were in the audience... forget what they called themselves but you can hear them screaming their heads off) but man do I love that album. I just cruised around youtube hoping someone had posted it in its entirety but alas only a couple of tunes and they are the much more normal ones...
https://www.youtube.com/watch?v=5pCiLPqoQsw https://www.youtube.com/watch?v=uZITQuE-_aI I should dig out the tape and digitize it because it has been years since I listened to the whole thing.
Other than that a lesser but still relatively well known in certain circles dude/act I own some material from is Feotus (JG Thirwell). I've only got the Sony release Gash and a live album they did called boil (both of which I paid pretty good money for). Their older stuff is extremely rare and much of it only available on vinyl. Markyzno is actually a fan which goes to show me how cool and diverse this forum is (BTW if you haven't heard Mark's album check it the frack out. It is in itself very cool and quite off the beaten path).
So yeah... I'm sure some of the older dudes probably have the AC album or have heard it (and I'm just gonna go ahead and assume craigB owns it) but if you want vintage live weirdness keep your eyes out for that one.
Honestly as a metalhead I bought it thinking it would be more traditional style Coop (which is pretty weird as it is) but ended up with... well... I don't know WTF that was. Art Death Prog?