Underestimated, song, artist or group '' gems'' ?

In any category of music you choose ( pop, opera, jazz, rock, folk - whatever ), I would like to find out about ''hidden gems'' - artists, groups or even songs and music that are not widely known or appreciated....you could include songwriters too.

I just feel that part of the excitement of discovering new music can also include past unknown gems that would be worth listening to....

Some of my ''underestimated'' favorites :

Many Elvis Costello tunes
Leonard Cohen's songs
Symphonic ''re-arrangements'' by Leppard in baroque music
The group ''Blue Rodeo''
The group (now extinct) Soul Attorneys - incredible, worth seeking out (Sony Music)