Finding Nemo is just terrific. I have watched it so many times, and it never gets old. Although the movies that preceded it were also terrific, this is where Pixar really started to hit their stride, to me.
Toy Story 3: If people want to learn how to write a trilogy without any of the three films falling flat or feeling like a sell-out or shark-jump, they really need to do an in-depth study on the Toy Story films. They are all fantastic. I am still amazed that they brought such brilliant closure to the series with this film.
Cars: Just fun, from start to finish. I love it.
Some of the others I was really struggling with that almost made the cut were Up, Inside Out, and Monsters, Inc. These were all close and just barely got edged out.
If I had to pick my three least favorite, Wall-E would definitely be my least. And I guess I would round out my "bottom 3" with A Bug's Life and Cars 2. But the problem is, I really enjoy both of those a lot and am only including them because the other films I have seen in the Pixar catalog are so strong (no comment on Dinosaur, since I have not seen it yet). For those that said they did not see Cars 2 because it looked like it wouldn't be any good, you are missing out. I liked it a lot.