Cartoon Network is streaming cartoons with their flash video player. The video player has volume control and a full screen option. There don't seem to be any commercials except those for Cartoon Network itself.

Stream Cartoons at CartoonNetwork.com

Here is a list of the cartoons that are currently streaming:

Bakugan
Ben 10
Bernard
Camp Lazlo
Chop Socky Chooks
Chowder
Class of 3000
Code Lyoko
Codename: Kids Next Door
Courage The Cowardly Dog
Cow and Chicken
Dexter's Laboratory
Ed
Edd n Eddy
Evil Con Carne
Foster's Home For Imaginary Friends
George of the Jungle
The Grim Adventures of Billy & Mandy
Johnny Bravo
The Mr. Men Show
My Gym Partner's a Monkey
Out of Jimmy's Head
The Powerpuff Girls
Squirrel Boy
Time Squad
Totally Spies