Okay, gonna try my luck with an 80's Marvel Ultimate Alliance cast.
Captain America:
George DiCenzo
Spider-Man:
Ronnie Schell
Wolverine: Pat Pinney (doing something similar to
Matt Mercer's Wolvie)
Thor:
Vic Perrin
Iron Man:
William Marshall
Daredevil:
Frank Welker
Deadpool:
Michael Des Barres (this voice and accent, but with the manic energy of his Murdoc)
Elektra:
Anne Lockhart
Ghost Rider:
Dick Gautier
Luke Cage:
Stanley Ross
Blade:
Dorian Harewood
Moon Knight:
Peter Mark Richman
Ms. Marvel:
Lisa Raggio
Spider-Woman:
Joan Van Ark
Black Panther:
Buster Jones
Mr. Fantastic:
Michael Rye
Invisible Woman:
Mona Marshall
Human Torch:
Jack DeLeon (?)
The Thing:
Mike McConnohie (this, but with a Bronx accent)
Silver Surfer:
Vic Perrin
Bruce Banner:
Michael Bell
Hulk:
Bob Holt
Doctor Strange:
Bill Woodson
Hawkeye:
Ronnie Schell
Professor X:
John Stephenson
Storm:
Andi Chapman
Sabretooth:
Bill Martin
Iceman:
Frank Welker
Colossus:
Dan Gilvezan
Cyclops:
Michael Bell
Jean Grey:
Libby Aubrey
Nightcrawler:
Neil Ross
Magneto:
Earl Boen
Nick Fury:
Richard Crenna
Hank Pym:
Jerry Houser
Wyatt Wingfoot:
Michael Ansara
Dum Dum Dugan:
Lance LeGault
Vision:
Frank Welker
Venom:
Bill Callaway
Black Widow:
Jennifer Darling (if you like Russian BW, just add a Russian accent to this voice)
Edwin Jarvis:
Andre Stojka
Weasel:
Ronnie Schell
Namor:
Bill Woodson
Namorita:
B.J. Ward
Ancient One:
Keye Luke
Clea:
Susan Silo
Wong:
Michael Yama (this, but a little less casual and slightly more mystical)
Lady Sif:
Mary McDonald Lewis (this, but with an "Asgardian" accent)
Valkyrie:
Linda Gary (this, but with an "Asgardian" accent)
Odin:
William Conrad
Balder:
John Vernon
Heimdall:
Dick Gautier
Hermod:
John Rhys-Davies
Uatu the Watcher:
Michael Rye
Lilandra Neramani:
Susan Blu
Crystal:
Sherry Alberoni
Gorgon:
Mike McConnohie
Medusa:
Diane Pershing (this, but mixed with the sultry sound of her Poison Ivy)
Triton:
Vic Perrin
Corsair:
Neil Ross
Dr. Doom:
Shepard Menken
Loki:
John Stephenson
Baron Mordo:
Stan Jones
Enchantress:
Janet Waldo (just add an "Asgardian" accent and a more femme-fatale sound)
Ultron:
Regis Cordic
Scorpion:
Neil Ross
Bullseye:
Michael Des Barres
Winter Soldier:
Charlie Adler
Radioactive Man:
Alan Oppenheimer
Fin Fang Foom:
Arthur Burghardt
MODOK:
Gregg Berger
Crimson Dynamo:
Earl Boen
Mysterio:
Peter Cullen
Byrrah:
Aron Kincaid
Krang:
Jeff Winkless
Attuma:
Henry Corden
Tiger Shark:
Joe Leahy
Mandarin:
Keye Luke
Grey Gargoyle:
Rene Auberjonois (this, but more evil)
Arcade:
Laurie Faso
Shocker:
John Stephenson
Rhino:
Ron Feinberg
Mephisto:
Ed Gilbert
Blackheart:
Stanley Ross
Lizard:
Alan Oppenheimer (this, but a bit more whispery, hissy and raspy)
Skurge the Executioner:
Dick Gautier
Kurse:
Tony Jay
Ymir:
John Stephenson
Piledriver:
Pat Fraley (this, but more evil)
Wrecker:
Ron Feinberg
Thunderball:
Stanley Ross
Bulldozer:
Ron Gans
Ulik:
Ed Gilbert
Deathbird:
Linda Gary
Warstar:
Arthur Burghardt
Hussar:
Jennifer Darling
Gladiator:
Earl Boen
Skrull Empress:
Mercedes McCambridge
Super Skrull:
William Marshall
Paibok:
Michael Rye
Galactus:
Lance LeGault