Concept art and colour scripts. "Many people don't realize we have almost as many artists at Pixar working in traditional media - hand drawing, painting, pastels, sculpture - as we do in digital media," notes John Lasseter in the programme Introduction to 'PIXAR 20 Years of Animation'. I'm looking through it planning storyboard classes for the 2nd year animators at SBIT.
One of the stand out artists is Lou Romano and he has a blog that shows his planning drawings as well as finished artwork. I'd advise researchers to scroll down until they at least find the colour script for "Up" from June 2009.
ARC history: A previous ARC post linked to Lou's work on "The Incredibles".