What started as an inside joke of CalArts alumni (a reference to the classroom number that was used by Animation students, including John Lasseter, Andrew Stanton, Brad Bird, Pete Docter) has been present in not only every Pixar film, but Disney movies, Iron Giant, The Simpsons, Family Guy, American Dad, Powerpuffgirls and Tinytoon Adventures.

2. Dug from UP in ratatouille

Its Dug from UP scaring Remy in ratatouille

3. PIzza Planet is everywhere

its the officialy delivery truck of PIxar. This delivery trucks appears in almost every movie in Pixar, showing up in Bug's Life, Incredibles, and Finding Nemo just to name a few. 

4. Buy N Large Battery from Wall E

Here we can see Buzz Lightyear using AA batteries to charge itself. If you look closely at the brand of batteries, 

It is actually Buy N Large the Mega Corporation from the movie in WALL E

5. Finding Nemo Cameo

6. Lots-o-Huggin Bear in UP

7. Doc Hudson in The Incredibles

8. Dinoco in Toy Story 1 

Now in Cars!

9 Carl and Ellie Fredickson's Postcard to Andy

Zoommm in

Here is Carl and Ellie in UP

10. The Pixar Trailer