I have found out by reading bios that alot of musicians started out as members of other bands i’ve listened to but didn’t know had the same member. So is there a list anywhere of all the famous singers and what famous band they started at?
Offhand i can think of
The Beatles - All except ringo had solo success
The police - sting
Genesis - phil collins
Take That - Robbie Williams
Nsync - Justin Timberlake
NWA - Eazy E, Ice Cube & Dr Dre
I’m sure there are hundreds more.
Rod Stewart- Small Faces
Peter Gabriel- Genesis
Stevie Nicks- Fleetwood Mac
Christine McVie- Fleetwood Mac
Michael Jackson- The Jackson Five
And FTR, Ringo Starr does quite well for himself. I think he’s definetly improved with age. 
Ringo has had some pretty decent success of his own. He gets no respect, but he ain’t broke. 
Also from Genesis - Peter Gabriel
Menudo ‘gave us’ Ricky Martin. The fuckers.
Annie Lennox – The Eurythmics
Black Sabbath- Ozzy Osbourne
Eagles- Don Henley, Joe Walsh
Led Zeppelin- Robert Plant
I don’t know if you would call it long-term success, but Mike Rutherford of Genesis went on to form Mike + The Mechanics. Lindsay Buckingham from Fleetwood Mac also had a fair solo run.
Natalie Merchant - 10,000 Maniacs
Debbie Harry - Blondie
Joan Jett - The Runaways
Belinda Carslile - The Go-Gos
Susanna Hoffs - The Bangles
Annie Lennox - The Eurythmics
Pink Floyd - Roger Waters
The Guess Who - Burton Cummings, Randy Bachman, Domenic Troiano
Max Webster - Kim Mitchell
Tranquility Base - Ian Thomas
Van Halen - Sammy Hagar (before and after)
As I think of more, I’ll check in later.
Destiny’s Child - Beyonce
D12 - Eminem (I think he started with them, but I could be wrong)
Was 2Pac originally a member of Digital Underground?
Gwen Stefani of No Doubt has a solo album in the works, which will be the last step of official induction in this thread.
I think he was a backup singer or backup dancer, not really a main member
Also from Genesis, Steve Hackett has had a solo career and was also part of GTR.
I think we can include the Yardbirds with Eric Clapton, Jeff Beck, and Jimmy Paige
Stray Cats - Brian Setzer
The Crickets - Buddy Holly
Yardbirds, Cream - Eric Clapton
(Oh yes, and for the record, Ringo Starr has multiple top 40 hits as a solo artist.)
Boz Scaggs – Steve Miller Band
Steve Winwood – Spencer Davis Group & Traffic
Pete Townsend (& to a lesser degree, John Entwistle and Roger Daltry) – The Who
Eric Clapton – John Mayall’s Bluesbreakers, Cream, Blind Faith, & Derek and the Dominoes
Robin Trower – Procul Harum
Paul Simon – Simon and Garfunkle
Elvin Bishop and Mike Bloomfield – Paul Butterfield’s Blues Band
Al Kooper – The Blues Project & Blood Sweat and Tears
Leon Russell – Gary Lewis and the Playboys & Mad Dogs and Englishmen
Alice Cooper – Alice Cooper (which was the band’s name before he went solo)
Joe Pesci – Joey Dee & the Starlighters
I forgot that David A. Stewart of the Eurythmics has had a fairly successful solo career doing scores for movies like The Ref and with tunes like Lily Was Here that he did with Candy Dulfur.
Mark Knopfler of Dire Straits has quite the second career writing movie soundtracks. I still have trouble keeping track of what he’s done.
Mark Mothersbaugh of Devo has followed the same path. That goes double (much more famously) for Danny Elfman of Oingo Boingo.
Britney Spears–The Mickey Mouse Club
Perhaps a bit more obscure, but still popular among some people:
Robin Hitchcock - The Soft Boys
Tanya Donnelly - The Breeders/Throwing Muses
Eliot Smith - Heatmiser
Paul McCartney - Wings
Melanie C and Geri Halliwell of the Spice Girls had a couple hits after they broke up.
Tricky - Massive Attack
Morrissey - The Smiths
KRS-One - Boogie Down Productions
Ricky Martin - Menudo
The Smiths begat Morrissey
The Misfits begat Danzig
Ben Folds Five begat Ben Folds
Til Tuesday begat Amie Mann
Generation X begat Billy Idol
Black Flag begat Henry Rollins
The Boomtown Rats begat Bob Geldof
Social Distortion begat Mike Ness
House of Pain begat Everlast
The Stooges begat Iggy Pop
James Brown (with his band) begat Maceo Parker and many others
The Vandals begat Josh Freese
The Commodores begat Lionel Ritchie
Velvet Underground begat Lou Reed
Soft Cell begat Mark Almond
The Pogues begat Shane McGowan
Talking Heads begat David Byrne
Y Kant Tori Reed begat Tori Amos