Horton Hatches the Egg

A film adaptation of the book of the same name by Dr. Seuss and a follow up to the film Dr. Seuss' Horton Hears a Who! was reported to be in production but nothing came of it.

Why It Was Cancelled

 * Presumably with Dr. Seuss' widow Audrey Geisel moving the film rights of other Dr. Seuss' projects to Illumination either in 2008 or 2009.