The group he played in, Rory Storm and the Hurricanes, was the biggest group in Liverpool for a time, but the Beatles had far surpassed them by the time Ringo was asked to join.
Bill Monroe and His Bluegrass Boys begat Lester Flatt and Earl Scruggs.
I think Iggy Pop is probably better known than The Stooges.
I’ve encountered people who were unaware that Neil Young was ever involved with Crosby, Stills, and Nash.
Actually, all of the original members of The Who released at least one solo album. Keith Moon’s Two Sides of the Moon wasn’t particularly successful and is of interest primarily as a novelty, though. Who needs an album of Moon singing, with most of the drumming done by others?
John Entwistle’s solo work had something of a cult following, but never really broke through to the mainstream. Roger Daltrey was rather more successful. I don’t think he ever cracked the Top 40, but he came close. But as you say, it was only Pete Townshend who had any real hits outside The Who. He’s also the only Who member ever to win a Grammy (for the Broadway Tommy album). The band itself, surprisingly enough, was never so honored by The National Academy of Recording Arts & Sciences.
And Caitlin Cary, who has had a couple of really great CDs.
New Edition begat solo careers for Bobby Brown, Ralph Tresvant, Johnny Gill & Michael Bivens as well as spinning out the group Bell Biv DeVoe.
Culture Club begat a modest solo career for Boy George.
Chris Perez began his career playing guitar in Los Dinos, the backing band of Selena, to whom he was eventually married.
Frieda from ABBA had at least one solo hit.
The Gumm Sisters begat Judy Garland 
Kim Deal never had a solo career, though. She played with The Breeders and The Amps, but never as Kim Deal.
I think that could fit- he did record the band’s first album all by his lonesome, save one guest guitar solo.
That’ “Frida” sweetie. And all the ABBA members have done post-ABBA work.
Benny&Bjorn scored moderate success with the musical “Chess” and mega-success with “Mamma Mia!” which they had very little to do with. I’m hoping the English version of “Kristina from Duvemala” will bring them the success they should have.
Agnethat released three solo albums, went into exile, took a stalker to court who turned out to be her ex-lover :eek: and recently released another CD “My Colouring Book.”
Prince and the Revolution begat Shiela E.
There was this group the Temptations that was lead by this Diana Ross lady… 
Vince Neil did a pair of albums after leaving Motley Crue.
Anyone meantion Lionel Richie from the Commodores? Of course, I blame him for the upcoming Paris Hilton album…
I think you mean the Supremes with Diane Ross…
As a great fan of Chess (well, at least of the Euro Concept Album), I was considering nominating Benny & Bjorn. But it didn’t really seem like they became solo artists, just clever Broadway collaborators. And for Mamma Mia, they did doubly little; their contributions to the adaptation to Broadway was minimal, and their original contribution was as members of ABBA, not post-ABBA.
Billy Joel was part of a group called The Hassles before he hit it big.
But, even better, he played in Attila, a power duo consisting of him on a B3 and a drummer.
Now I have to find me a copy…
Frankie Valli had a nice solo run in the 70s after his time with the Four Seasons.
Eddie Kendricks had a Billboard #1 in the U.S. after leaving the Temptations. Smokie Robinson also did well after leaving the Miracles.
Guitar virtuoso Steve Vai has been a popular live headliner for years, thought none of his solo work has made the American Top 40. His name was made mostly after his stints in Frank Zappa’s and David Lee Roth’s bands.
Michael Nesmith had a fairly decent solo career (mostly C&W) after The Monkees. Not to mention his producing credits.
The Fresh Prince left DJ Jazzy Jeff and managed to make a niche for himself as an actor, didn’t he?