Too many favorites to list one...
Powerpuff Girls, Dexter's Laboratory, Ed, Edd n' Eddy, Cow and Chicken, Courage the Cowardly Dog, Sheep in the Big City, Foster's Home For Imaginary Friends, The Grim Adventures of Billy and Mandy, Teen Titans, The Misadventures of Flapjack, The Looney Toons Show, and The Amazing World of Gumball (mostly for its creativity... the humor's pretty lame sometimes). I guess Adventure Time is also creative, but the use of words just annoys me too much to watch it. >.> The 90's and early 2000 shows were really the best ones though, imo.