Does anyone remember the Toy Story 2 teaser? It was the same thing: centered around the characters bringing in the title, then Woody and Buzz bicker for a little bit, then presto! release date, and out. It's pretty much a perfect teaser--no plot spoilers, just saying "hey, the gang's back, be there!" And for Toy Story, that's all anyone should need.
EDIT: I tried to do a search for them, but came up empty handed. Did find this cute TOY STORY/WALL*E commercial that I hadn't seen before: http://www.youtube.com/watch?v=GEL0tZC-2ew