Everybody wants to see the Toy Story 3 trailer as soon as possible, and many were hoping that it would be attached to Pixar's Up, coming out this summer, but, I am sorry to disappoint them, but the TS3 trailer will just have to wait.
Now that Walt Disney Animation Studios and Pixar are both under Disney, they are more than likely going to have a sort of 'trailer-pattern'. Let me explain: Disney's The Princess and the Frog will precede Pixar's Up, since the next Disney release after Up is The Princess and the Frog. (So, also be sure to spot the Up trailer before Race to Witch Mountain, which is a Disney film that comes out today).
If this pattern pans out like I think it will, we should expect to finally see the Toy Story 3 trailer before The Princess and Frog, which was just recently assigned an earlier release date of December 11 of this year.