Mostly Punk, Post-Punk, New Wave, Synth-pop, Industrial, EBM, Alternative, folk rock, Goth Rock, early Grunge, Brit Pop, Alternative-dance, Indie rock, etc. releases prior to 1992, the debut of Chicago's Q101 as an alternative rock station. However, there are a few tracks lists that released in 1992 or later.

sources:
http://www.rocklists.com/alltime42.html
http://www.rocklists.com/alltime33.html