Those little shorts Pixar puts before for each of their movies are fantastic. I love watching these things. My kids' favorite is probably Jack Jack Attack, the back story of what happened with the baby-sitter during the Incredibles movie (though Presto is a close second). I think my favorite is Boundin', which always sets me right when I start feeling sorry for myself. The short from Brave, La Luna, is now available online. As a dad, this one gets to me every time I watch it.
As an aside, the I was pleased to see Disney put a short at the beginning of Wreck-It Ralph, Paperman which is, in my opinion, Pixar caliber.