If you go early, right at opening (or a little earlier because they open Main Street first), there are often several characters right at the front of Main Street. (i.e. M&M, Goofy, Donald, Daisy, Tigger, Chip & Dale...) You will find princesses at Snow White's Grotto (to the right of the castle when you are facing it) usually starting around 10:30am, I think, and there is also a hidden spot to the left of the castle behind the Royal Banquet Hall that you will also find people like Rapunzel, Anna & Elsa etc, but I've never pinned down when exactly they are there. We always seem to just miss them. Inside Fantasyland, there are the Fantasy Gardens where you can get Minnie, Mickey, Winnie the Pooh, and a few others, I think, and that's usually busy in the afternoons. In Toy Story Land there is a designated spot where you can meet Woody, Jessie, Lotso etc, usually in the afternoon. In Tomorrowland you can meet Buzz Lightyear in the lefthand corner of Comet Cafe next to the Buzz Lightyear Astroblasters ride. In Grizzly Gulch, you can meet Chip and Dale across from the restrooms toward Mystic Manor.