I have a VERY complete ABC list of Disney things, send me a private message with your email and I'll forward it to you if you like. It's not just characters, but WDW places too. But for now here are a few ideas for the letters you are having trouble with:
I: Indiana Jones, ice cream, It's Tough to Be a Bug, Innoventions, International Gateway, Ice Station Cool, Illuminations, It's a Small World
K: King Louie, Kanga, Kermit, King Triton, Kali River Rapids, Kilimanjaro Safaris
O: Oliver, O'Malley, Owl, Oasis, Orlando, Osborne Family Lights
X: x-ray (there's a cool visual prop in WoL)
Y: Yacht Club, Yachtsman Steakhouse
Z: Zeus, Emperor Zurg, Zip-a-dee-doo-dah, Zazu and of course Zzzzz