Lots of choices for this of course. Simple rule, song can't be released as a single. Wikipedia is a great source for this btw. Go to a band and their discography.
Foo Fighters - Hey Johnny Park
Foo Fighters - Baker Street
Pearl Jam - Black
ok this is kinda cheating since this song actually charted very high on rock chard but it's not a single so count it.
Pearl Jam - Tremor Christ
Another Cheat. Pearl Jam only released, 11 singles from their first 3 albums which are all amazing and have some of the best songs of 90s on them.
Pearl Jam - Long Road
This one didn't chart, and almost always makes my eyes water.
I'm stopping with Pearl Jam cause I can go on for days.
For Metallica I'm gonna keep this clean, since they only released 1 song each from Master of Puppets and Ride the lightning I'll pick my favorite song from each album not released
Metallica - Fade to Black
Metallica - Welcome Home (Sanitarium)
Led Zeppelin they only released 25 songs. Including B-Sides. So I'm limiting myself to 3 of theirs
When the Levee Breaks
The Rain Song
BTW it's a shame for the single this wasn't released instead of Whole Lotta Love, or should have let Whole lotta love go with another and release this with Living Loving Maid because these 2 go together like Peanut Butter and Ladies.
I'm stopping for now but I'll be adding more I'm sure.