From Thomas H. Smith:

In Honor of the 99th anniversary of the Walt Disney Studios, I have made a mega compilation of all the voice actors behind the characters up until their 54th anniversary. Or at least the ones I could find footage of.

Cast In Order Of Appearance:
Walt Disney as Mickey Mouse
Billy Bletcher as Pete
Florence Gill as Clara Cluck
Clarence “Ducky” Nash as Donald Duck
Pinto Colvig as The Big Bad Wolf
Jimmy MacDonald as Sound Effects
Milt Kahl as Ferdinand the Bull
Adriana Caselotti as Snow White
Harry Stockwell as Prince Florian
Cliff Edwards as Jiminy Cricket
Frances Gifford as Casey Jr.
Nicky Stewart as Brer Bear
Ilene Woods as Cinderella
Eleanor Audley as Lady Tremaine and Maleficent
Kathryn Beaumont as Alice
Sterling Holloway as The Cheshire Cat
Ed Wynn as The Mad Hatter
“Professor” Jerry Colonna as The March Hare
Hans Conried as Captain Hook
Barbara Luddy as Lady
Bill Thompson as Jock
Bill Baucom as Trusty
Peggy Lee as The Siamese Cats and Peg
The Mellomen as The Dog Chorus
Louis Prima as King Louie
Paul Winchell as Tigger

[Thomas H. Smith | Via BIS]