Over 30 gigs of 1980s underground music cassettes have been posted at Archive.org. The tapes, most of which are of rare and unknown bands, cover most "alternative" genres including punk, post-punk, indie, garage rock, goth, industrial and a lot of other stuff. The majority of the tapes were donated to the project by former CKLN FM radio host Myke Dyer in August of 2009.

You can start digging through the tapes here.