Be sure to head over to Frontierland in MK, that is cowboy central! There is a Woody's Round-up Show, not sure of its exact name but its what my kids call it, that takes place there a few times each day, just ask a Cast Member for times, not sure its on the park schedule but if it is someone on here will correct me. The Show is interactive with kids and parents alike and you will find Woody, Jessie and even Bullseye there too, they are also out for autographs in that area each day too. In Tomorrowland you will find Buzz signing autographs near the Buzz ride too.
Over in Hollywood Studios, you will find characters in Pixar Alley, right across the way from the new Toy Story Mania ride, there is now an enclosed area for autographs ...again check your time schedule to see when to get in line! Word of advice, if you plan to get on Toy Story Mania ...get in line as soon as the park opens or atleast get your FP tickets for a later return, its a very popular ride!!!