Eric Tan's Poster Art.

Eric Tan creates posters for Pixar.  On his work, he says: 

"The bright colors and flat shapes were inspired by the Disneyland attraction posters you see when going through the tunnels at the entrance of the park. Even when I was 6, I remember thinking those things were amazing, so getting to reference them for this project was a thrill in itself."

I love those old Disney posters too, Eric.  See more examples of Tan's work here and here.