This site , by DIS member HugsForEeyore, has a pretty exhaustive list of characters, as well as frequency of appearance per personal experience
At the WDW website, click the
FAQ under any park. It doesn't list every single character, as they vary by day and time of year, but it gives you a good idea.
Magic Kingdom
Mickey's Toontown Fair
Mickey's Country House: Mickey Mouse
Toontown Hall of Fame Tent: Minnie Mouse and others
Adventureland
Congoasis: Rafiki, Timon, Baloo and King Louie
Fantasyland
Mad Tea Party
Fantasyland Character Festival
Frontierland®
Splash Mountain: Brer Fox and Brer Bear
Epcot®
Always get the latest Times Guide at Guest Relations. Discover the Characters in a number of locations, including:
The American Adventure
The America Gardens Theatre, daily
World Showcase
The Germany, Morocco and United Kingdom Pavilions, plus the International Gateway and Showcase Plaza
Disney's Hollywood Studios™
Always get the latest Times Guide at Crossroads of the World.
Animation Courtyard
Mickey Mouse and other Disney Characters
New York Street
Al's Toy Barn: Buzz, Woody and more.
Disney's Animal Kingdom® Theme Park
Visit Camp Minnie-Mickey, an old-fashioned summer camp where the characters go when they're on vacation. Throughout the day, this is where you'll find Mickey and his pals waiting to greet you!