Well, I have seen the following at the Magic Kingdom:
Mickey, Minnie, Donald, Daisy, Goofy, Pluto, Cinderella, Snow White, Aurora, Belle, Jasmine, Ariel, the seven dwarfs, Brer Bear, Pooh, Tigger, Eeyore, Capt Hook, Jafar, Genie, Aladdin, Peter Pan, Wendy, Smee, Baloo, King Louie, Mowgli, Alice, Tweedle Dee and Tweedle Dum, the White Rabbit, the Mad Hatter, Buzz Lightyear, Chip and Dale, Stitch, Frollo,
At Epcot we have seen Belle and the Beast, Mary Poppins, Pooh, Tigger and Eeyore, Jasmine, Aladdin and Genie, Snow White and Dopey, Mulan, Chip and Dale, King Louie, Baloo, Mickey, Minnie, Goofy, Donald, Pluto.
At Disney MGM we have seen Buzz Lightyear, Woody and Jessie, Playhouse Disney characters, Lilo and Stitch, Mulan and Shan, the Incredibles, Sorcerer Mickey, Pooh, Tigger, Eeyore, Esmerelda, Megara, Hercules
At Animal Kingdom we have seen Thumper, Lilo and Stitch, Mickey, Minnie, Pluto, Goofy, Donald, Daisy, Pooh, Tigger, Eeyore, Baloo, King Louie, Rafiki, Pocohontas, Jane, DeVine and others.
This, of course, has been over the years, so not all of these characters may be there everyday, however, if you stop by Guest Relations on your way into the park, if there are specific characters in which you are interested, you can ask where and when they are scheduled to appear.