Toy Story 3 director Lee Unkrich announced he has begun a new project via his Twitter page:

Lee Unkrich Tweet
"Today is day one on my next project. Every day I'll post a new photo chronicling the journey. #UnkADay"

Last week, the director wrote "tomorrow is a big day that may determine the next four years of my life. Wish me luck," so it looks like the director is moving forward with the project that might get released around 2015.

No word on what kind of film it is, except that it's in the scripting phase.