For me it’s Roger Daltry on vocals, Frank Zappa and Mark Knopfler on guitar, John Entwhistle on bass, and Levon Helm on drums. I’m not sure they’d mesh very well. Roger and John would obviously be fine. Knopfler and Levon probably would as well. Could any of them work with a perfectionist like Zappa? Maybe Knopfler, but I don’t know about the others. For the purpose of this exercise those who are in rock and roll heaven live again.
If you put Tommy Makem and J. S. Bach together in a room and told them to jam, I’m sure they’d come up with something interesting, but I have no friggin’ clue what it’d be.
Terry Kath and Steve Lukather on guitar, Geddy Lee on bass and keyboards, and Jeff Porcaro on drums. Kath, Luke and Lee share vocals. All of them can play just about any style so I think it works. They’d be more of a “musicians” band like Kings X or Dream Theater.
Bob Dylan, Tom Waits, Mark E. Smith and Laura Nyro. No problem.
Hmmm this raises interesting possibilities…
Michael Jackson performing with KISS? The King of Pop singing "Detroit Rock City’ and “I was Made for Loving You”? Gene and Paul performing “Beat It” and “Bad”?
Johnny Cash performing with Metallica? Cash performing the vocals on “One” and “Enter Sandman”? Hetfield and the boys performing “The Man comes Around” and “Ain’t No Grave”?
These possibilities are endless…
Guitar 1- Johnny Marr
Guitar 2- Kristin Hersh
Bass - Kim Deal
Vocals - Kimbra
Keyboards - Martin Gore
Drums - Doktor Avalanche
I can see that working out just fine.
For the past several years my interest is in bluegrass/country/oldtime music. One of the wonderful things about that type of music is that the absolute best musicians frequently team up with each other - and magic occurs. Just the other day I was listening to a bunch of Doc Watson (guitar) picking w/ Bill Monroe (mando). I play upright bass, and no one does it better than Edgar Meyer - who has played with EVERYONE. Bruce Molsky (fiddle), Sam Bush (mando), Ricky Skaggs (anything he happens to pick up) play with any number of super combos, both large and small.
Hell, it is so common, Marty Stuart wven call his band The Fabulous Superlatives! 
Rhiannon Giddens - would be an addition to ANY group in ANY style. And my 2 current pave flatpickers are Billy Strings and Molly Tuttle. Again - virtuosos who add to any gathering of musicians.
Well, lemme see, just of the top of my head I try to gather a band of my favorites:
James Burton - lead guitar
Malcolm Young - rhythm guitar
John Entwhistle - bass guitar
Garth Hudson - keyboards
Aretha Franklin - vocals and piano
Could definitely work. Dream band for me.
I saw Rush perform with Public Enemy. If they want it to, it’ll work.
If Sandy Denny can sing with Led Zeppelin, anything is possible.
Vocals, Female - Sandy Denny, Annie Haslam, Grace Slick
Vocals, Male - Marty Balin, Freddy Mercury
Guitars - Carlos Santana, Richard Thompson, Glen Campbell
Bass - John McVie
Drums - Mick Fleetwood, Max Weinberg
Percussion - Ray Cooper
Keyboards - Chick Corea, Roy Bittan
Shit, I forgot the drummer. Keith Moon.
What an absolutely glorious trainwreck that would be 
AAAAARGHHH! Entwistle!
“idiosyncratic” could be a word for it.
Had Mark E. Smith lived, given his turnover rate it was a nailed-on certainty that those others would have to be in The Fall at some point. There are only so many musicians in the world.
Here’s one that might work. Perhaps not my absolute top picks in every category but certainly artists I very much enjoy. Not allowing multiple choices from the same group and choosing on the basis of what I think could be a meeting of musical styles. I’m thinking precision, driving rythymn and melody.
2 keyboardists, Micheal Rother (Neu! Kraftwerk and Harmonia) and Brian Eno (err…it’s Brian Bloody Eno)
Drums - Stephen Morris (Joy Division, New Order)
Rythmn Guitar - Lyndsey Buckingham (Fleetwood Mac)
Lead Guitar - Dave Gilmour, (Pink Floyd)
Bass - Nikki Monninger (Silversun Pickups)
oops, duplicate post, it was good but not *that *good.
Not Laura, sadly.
Alex Lifeson on Guitar
Phil Collins on Drums
Kim Warnick (the Fastbacks) on Bass and backing Vocals
Trent Reznor on Keyboards
and to round it all off…
Robin Zander on lead Vocals.
Alex and Trent will handle songwriting. Phil will not be allowed in the room.