This is not a complete comprehensive list by any means. The actors listed below voiced many more characters, too many to list here; these are some of the more well known or recognized characters. Many of these people are also writers, screen actors, producers, and directors.
If you thought Popeye, Babe and Bart Simpson were voiced by men, think again. It turns out that many male cartoons are done by women and female characters are voiced by men.
Pokemon
Veronica Taylor as Ash Ketchum
The Boondocks
Regina King as The Freeman Brothers
Babe: Pig In The Big City
Elizabeth Daily as Babe
Arthur
Robert Naylor as DW
The Simpsons
James Earl Jones as Maggie Simpson
Dragonball Z
Colleen Clinkenbeard as Gohan
The Simpsons, also voiced Ralph and several other minor characters
Nancy Cartwright as Bart Simpson
South Park
Trey Parker as Ms Choksondik
The Muppets
Frank Oz as Miss Piggy
Dexter's Lab, also appeared on Rugrats as Chuckie Finster.
Christine Cavanaugh as Dexter
Rocko's Modern Life
Charles Adler as Bev Bighead
Jimmy Neutron
Debi Derryberry as Jimmy Neutron
Popeye
Mae Questel as Popeye
Fairly Oddparents
Tara Strong as Timmy Turner
King Of The Hill
Pamela Aldon as Bobby Hill
Now Cartoon Voice Actors of the Past:
Click to enlarge.