Here are a list of the more common South Park characters their voice.

Matt Stone:
Kyle
Kenny
Butters
Tweek
Gerald Broflovski
Stuart McCormick
Jimbo
Jesus
Saddam Hussein
Pip
Terrance

Trey Parker:
Stan
Cartman
Timmy
Randy Marsh
Grandpa Marsh
Big Gay Al
Craig
Dr. Alphonse Mephesto
Mr. Garrison
Mr. Hankey
Mr. Mackey
Miss Choksondik
Phillip
Jimmy
Satan
Officer Barbrady

Isaac Hayes:
Chef

Adrien Beard:
Token

April Stewart:
Liane Cartman
Sharon Marsh
Mrs. McCormick
Shelley Marsh
The Mayor
Principal Victoria
Mrs. Crabtree