Well, assuming that this means the golden age of sound theatricals in the USA, here goes
Walt Disney (thru Universal, Pat Powers*, Columbia, United Artists, RKO-Radio Pictures and then finally self-distributed since 1953**)
Warners-Harman-Ising then Schesinger then in-house, then DFE*** and Format Films then again in-house
MGM-Harman-Ising then in-house then Snyder-Deitch then C.M.Jones-Tower 12-Sib
Max Fleischer (thru Paramount)
Paul Terry (thru Educational and then Fox)
Walter Lantz (thru Universal (International)^ )
Ub Iwerks (thru Celebrity and MGM)^^
UPA (thru Columbia and in the case of the feature from 1962, "Gay Purr-ee", Warner Bros., only Jack Warner didn't expect it, tee-hee!)
Paramount Famous (rebranded Harveytoons since 1957 due, of course, to Harvey Comics's deal with the studio since the 40s.Replaced Fleischer).
Van Buren (one of the the smallest, forgot the distributor but based out of New York)
*One of Disney's very early distribution deals was what was called a "states's rights basis", though I've never too sure of how it went but it was
an independent kind of deal..
**The Disney self-distributing company maintained since 1953 is Buena Vista-it's even listed in Box Office Mojo and other sites
***DePatie-Freleng, who already had their :Pink Panthers and other non-Looney-Merrie shorts released thru United Artists-while for a few years BEING ON the WARNER BROS.LOT!!(They moved off around 1966-1967.)
^:Lantz:And thru United Artists for a while in 1950-51.
^^:Ub Iwerks, of course, was the top secret brains behind Disney's inventions, one of those many Disney magicians who became Disney Legends (kinda like Walt's short "Ben and Me",1953, isn't it.:-))
Hope that helps!