Let me see if I can remember who and where we've seen them.....
Princess Breakfast at Plaza Inn - Fairy Godmother, Cinderella, Princess Aurora, Snow White, Belle, Beast, Aladdin, Jasmin, Mary Poppins, Burt
Goofy's Kitchen - Goofy, Pluto, Baloo, Aladdin, Donald, Alice, Mad Hatter - it seems like there should be more, but I can't remember right now
In
Disneyland
Main Street - Alice, Mad Hatter, Queen of Hearts (these 3 are usually right at the gates just before opening), Mickey, Minnie, Goofy, Pluto, Mary Poppins, Burt, Nigel (the penquin), Chip n Dale (not usually all at the same time, but at various times throughout the day)
Castle Hub - Belle, Beast, Cinderella, Prince Charming, Princess Aurora, Prince Philip, Snow White
Matterhorn side of the castle - Wendy, Peter Pan and Captain Hook
Frontierland - Woody, Jesse, Goofy (in western wear), Pluto
Critter Country - Pooh, Eeyore, Tigger, and sometimes Piglet
Toontown - Mickey, Minnie, Goofy, Pluto, Donald, Daisy
Tomorrowland - Buzz (but this used to be after his show which is no longer running, not sure where you'll find him now, probably near his ride)
In California Adventure
Sunwheel Plaza - Minnie, Pluto, Donald
Hollywood Pictures Backlot - Mr Incredible, Elastigirl, Frozone
Animation Building - Stitch, Snow White, Princess Aurora, Cinderella
Paradise Pier - Lilo and Stitch
Redwood Creek Challenge - Meeko, Koda, Kanai, Tirk
I know there are more probably more characters but we don't usually see many in CA. Then again, we usually do all our character hunting in DL.