On reddit this was always bait for people who don't know what "mainstream" or "underrated" means. Like I don't know if you've heard of this obscure niche ragtag band... Supertramp? Compare Andrew Garfield's Spider-Man treating every cultural touchstone from prior to 2000 as lost knowledge found in ancient manuscripts.

So I'm gonna say Kingston Wall, a Finnish progressive rock band, and risk finding out that they were a household name for the dozens of people who gave a shit about prog in the 90s. "We Cannot Move" sounds like the pinnacle of 70s production. It just came out while Yes was doing synth-pop and Pink Floyd was doing a Moody Blues album. If it turns out everyone who's heard of Porcupine Tree already knows about them... good.

If we're talking mass appeal that's missing, I'd say The Cinematics. Two and a half albums of energetic alternative rock. Broadly anti-consumerist messages throughout. Guest work from We Are Scientists and Beck. Broke up for unspecified reasons. They deserve to be one of those "oh yeah, those guys" kind of bands. Not mindblowing... but remembered.

Yes thanks.

Some that I think should be wayy more popular than they currently are:

• Jukebox the ghost
• aimee mann
• V.A.S.T
• Prefab sprout
• Ivy
• Passion pit
• Placebo
• The war on drugs
• tokyo police club
• Stars
• The dismemberment plan

In case my posting history (and in fact user name lol) doesn't make it obvious - Infected Mushroom

It's impossible to pick a single example or a favourite track, since they vary so widely in style and it depends on what mood your in! But some of the better known classics are (best heard on headphones, unless you have a really incredible audio system):

Bust A Move

Heavyweight

The Messenger

Cities Of The Future

And one from their 25th anniversary album
A Cookie From Space

And many many more in between, but I'll leave it at that lol (E: the links are each from the full album playlist, so that's a good place to start)

Days N Daze

Mdou Moctar

I've been big on MUTEMATH since highschool. Unfortunately, I think they've broken up, but I still love their music.

So many artists, but as a huge metalhead here are two who IMO deserve way more light.

Ruins of Beverast https://theruinsofbeverast.bandcamp.com/album/exuvia

Worm https://20buckspin.bandcamp.com/album/foreverglade

Clown Core

Umphrey’s McGee

The longest johns

Sleep Token. They're not as obscure as they used to be. They kind of blew up this year but only in the metal scene. Not quite mainstream yet but I think they'll get there.

AURORA, although I guess she's gaining increased mainstream recognition now?

Since I'm very hurdy gurdy focused atm, Patty Gurdy and Michalina Malisz (as well as her band LYRRE)

Nulberry

(Now called "The She Gulls")

Very talented mathrock artist.

Kaitlyn Aurelia Smith

Cari Cari (just discovered them, psychedelic jams)
Bargain Music (reggae/ska, similar to sublime)
Secret Chiefs 3 (schitzo alternative/middle eastern, many members of Mr. Bungle)
TR/ST (darkwave)
The Two Man Gentleman Band (old timey barbershop banjo)
Superorganism (psychedelic)
Me First and the Gimme Gimmes (punk covers)
St. Vincent (indie/alternative)

Tigran Hamasyan (Armenian piano jazz-metal)

The Gabriel Construct (self-described as art music iirc, but basically just some experimental rock)

Jaggery (avant-rock, cool harp sounds)

Noah Sias (deathcore? Just so fucking heavy idk)

Bent Knee (experimental rock, just an absolutely gorgeous song)

Mel Bryant (indie rock, great hook, cool breakdown)

Mutemath is one of my favorites. Every album is different. In recent years they got more electronic sounding and the band broke up a couple of years ago.

LūN (EDM)/Lights (electropop) (same artist, different personas) has some great music if you'll like that kind of stuff. Probably most recognized in Canada, much less so in the US and rest of the world.

I also enjoy Echo Movement (reggae) but I'm not sure if they're still making music or not.

All links go to invidious.

Watsky!

Atomship. It was a blend of alternative metal and progressive rock. It's a really unique sound and they only ever did a single album.

Poets Of The Fall. They aren't too known but they are the ones behind many Remedy games soundtracks including Control and Alan Wake. Dam they're good, especially their Alexander Theatre session and live performances.

FKJ (French Kiwi Juice)

Dude is incredible, and his Cercle set is breathtaking.

Many... too many to list.

Orbit Culture's great if you're a metalhead

Idk if it's mainstream or not, but I really like Winona Fighter. Good angry punk rock.

Nightly. But they are getting there.

The Japanese metal band Galneryus

Papadosio.

vexento

Collective Soul (fairly popular in their heyday, less so now)