There was a kind of serendipity, though, to what good radio DJs/playlists could introduce you to. I also spent a lot of money on compilations, some of which were curated quite well by labels (like Subpop and SST), record stores (Newbury Comics in Boston), and fanzines (Flipside).
Other sources for discovering good music included friends' record/CD collections, live shows, publications of varying quality, and (I hate to say it) MTV.
Some of these sources were controlled by the music industry, but there were ways for some really interesting and great music from unknowns to float to the surface.
Music stores were a primary source of discovery for me as well. I was introduced to my favorite band after my friend heard their CD playing at a music store.
Bigger stores often had listening stations where they would feature CDs with headphones so you could hear them before you buy. I got introduced to some amazing albums via that process.
I lived overseas in the 90s and radio there was pretty bad, but those listening stations at the local Tower Records kept me connected to English-language music and introduced me to some fantastic albums and artists, including NAS, The Verve, DJ Guru, and The Presidents of the United States of America.
Other sources for discovering good music included friends' record/CD collections, live shows, publications of varying quality, and (I hate to say it) MTV.
Some of these sources were controlled by the music industry, but there were ways for some really interesting and great music from unknowns to float to the surface.