I’m loving this!!
So many.bands I’ve never heard of ! 
Sent from my SM-N910V using Tapatalk
Gary and the Hornets, no doubt the inspiration for Cream 
The Band Perry. Being siblings might help.
43 posts and no mention of the most famous and successful female trio of all time The Supremes???
Local favorite: Aliotta Haynes and Jeremiah
The Casual Dots
The Cave Weddings
The Cigarettes
The Coathangers
Screaming Females
Shannon and the Clams
The Clears
Cocteau Twins
The Cosmetics
Crash Course in Science
Magic Hour (Galaxie 500 fans, Damon and Naomi were in this)
Damon & Naomi with Ghost
The Cure (first album, only)
It’s even more complicated! Reynolds was out of the band before they became successful, but they kept their old name, rather than becoming “Hamilton, Joe Frank, and Dennison.”
The greatest Welsh metal band ever: Budgie!
To be sure, that’s a minor distinction, like “Greatest Female Nose Tackle” or “Greatest Japanese Power Forward.”
The Thermals
The Joy Formidable
Biffy Clyro
The XX
Nada Surf
The Secret Machines
Alkaline Trio
Hüsker Dü
Muse
Peter Bjorn and John
Them Crooked Vultures
Sebadoh
Band of Skulls
Sugar
Everclear
The Fratellis
Silverchair
Low
Feeder
Thirty Seconds to Mars
Bratmobile
Triggerfinger
Elliott Brood
Manic Street Preachers
Yeah Yeah Yeahs
Failure
The Presidents of the United States of America
Two Door Cinema Club
Placebo
Dispatch
Menomena
Paramore
The Wombats
Timbuk3, though they later added a fourth member. At their height they were in the movie DOA with Quaid and Ryan, playing “Too Much Sex, Not Enough Affection” but they’re probably best known for “The Future’s So Bright I Gotta Wear Shades.”
The Black Eyed Peas up until they added Fergie (who many forget was a member before going solo).
Damn, it took that long for the biggest thing since powdered milk to be mentioned? How sad.
Frank Marino & Mahogany Rush were a 3 piece for a long time.
Occasionally Frank’s brother Vincent would play along with them as rhythm guitarist.
Opal: David Roback (Rain Parade), Kendra Smith (Dream Syndicate), Keith Mitchell (Green On Red). Awesome neo-psychedelia! One of the favorite “local” LA bands from my teens. Wore out my Happy Nightmare Baby cassette a few times.
After Kendra left, went on to become Mazzy Star when Hope Sandoval replaced her on vox.
Sent from my XT1045 using Tapatalk
Marcy Playground, anyone heard of them?
What about Cluster (Roedelius, Moebius[sup]*[/sup], Plank)? They did do a lot of collaborations, though, so maybe it was never really a 3-person band.
*not the French guy who drew Harzac
The Shaggs.
You know the drill.
Rapeman
OTTG:p
Hate Eternal
Ed Hall
Bitch Magnet
Soy:p
Bastro
Krisiun
can’t remember if pre-Harrison Talking Heads were mentioned
Blind Idiot God
fantastic band from Sweden called Nasum whose guitarist/founder sadly perished in the Indian Ocean tsunami.
Nomeansno
Victims Family
Rhythm Pigs
Another 10 minutes this list would be twice as long so I’ll just ease up, with the hopes there won’t be any coming-up threads with 4-member bands.
I love Opal. Have you heard their Early Recordings compilations? Possibly even better than the album. Check out Lisa’s Funeral and Cherry Jam.
Datblygu Weirdo DIY punk, in Welsh!
The Homosexuals
Dead Moon (see also, The Rats and Pierced Arrows)
Deee-Lite
De La Soul
The Dodos
The Tunnel Runners
Dreamend
Drinking Electricity
Dusk to Dawn
From the 80’s revival until Davy Jones died, the Monkees was usually the trio of Mickey, Peter, and Davy. Mike was usually too busy to join in, tho there were a few times.
Jethro Tull in the late '80s: Ian Anderson, Martin Barre, David Pegg.
Peter, Paul and Mary (mentioned upthread) had two incarnations, one lasting nine years and the other 31; there was an eight year break.
ZZ Top (also mentioned upthread) has been a stable trio since 1973, and had existed in some form for four years prior to that.
Oh! Did anyone mention the Roches? They performed mostly as a trio from 1976 until last year, when Maggie died