To start, let's begin with Neutral Milk Hotel. I will list each release, and add a little blurb with my thoughts on them. The entire band only actually existed on In the Aeroplane Over the Sea. On all other releases, it is only Jeff Mangum with help from various random people.
Neutral Milk Hotel Releases
Invent Yourself a Shortcake (1991)
This demo tape is very early, with very harsh audio quality, but there are also weird tracks that almost just seem like a random selection of field recordings including one that appears to be Jeff Mangum making a prank call to a sex hotline. The music isn't the best, but it's charming. A few tracks are recognizable, and if you're interested in their history, I would recommend looking into the band Synthetic Flying Machine.
Favorite track: Prank Call