In France, you'll usually find Belle dressed in her blue village dress. She's usually near the water across from the Chefs de France restaurant, and sometimes the Beast is with her.
At Toontown Hall of Fame, Belle usually appears in her gold ballgown. Lines can get pretty long here, so you'd probably want to get there around when it opens at 10am. Also, Belle is never guaranteed, but when you enter the Hall of Fame, they list what characters are making appearences in each of the rooms. If Belle's picture is on the sign above the line, that means she's there that day.
Marie is sometimes in France in the garden near the perfume shop, but not always.
Peter Pan is usually in Adventureland near the Pirates of the Caribbean (Just to the right of the shop in a little alcove). Wendy is usually with him.
I've had fairly bad luck finding Chicken Little, but I heard that he has been in Town Square at MK lately. As for the Princes, they're mainly only out for special events. Prince Charming is usually at the character dinner at 1900 Park Faire, and Aladdin (not in his Prince Ali outfit though) can be found in Morocco at EPCOT and near the Magic Carpets in MK.