Pixar's logo has changed quite a bit over the years. Jay Orca combined a lot of them into this wonderful 3-minute video showing the history of Pixar's logo.

The full list of opening credits:
1. Pixar Animation Studios (1986, with fanfare, taken from Luxo Jr.)
2. Pixar Animation Studios (1987, taken from Red's Dream)
3. Pixar Animation Studios (1988, taken from Tin Toy)
4. Pixar Animation Studios (1989, taken from Knick Knack)
5. Pixar Animation Studios (1995, first seen at the end of Toy Story)
6. Pixar Animation Studios (2006, Celebrating 20 Years variant, taken from Cars)
7. Pixar Animation Studios (2009, 3D variant, first seen on Up)
8. Pixar Animation Studios (2011, Celebrating 25 Years variant, taken from theatrical prints of Cars 2,
9. Pixar Animation Studios 3D Variant was seen on Toy Story 2
10. Pixar Animation Studios Logo was Taken from Toy Story 3

[Jay Orca via Kottke]