While I doubt she would ever go into the business, I would LOVE for K.T. Grey (who voiced Seras Victoria of Hellsing) to voice a Disney princess. Then again, she's my favorite voice actress in general.
Jenna Ushkowitz from Glee has a very pretty, Disney Princess-y voice. She literally sounds like a Disney Princess when she sings, especially here www.youtube.com/watch?v=zQ5cWdFyWK8
If I'm being completely honest, then Myself. I really wanna be a disney princess but I sing like crap sooooo.....but if I have to pick a 'celebrity' or whatever than Candice Glover, I think she'd be a good black princess. She has one of the best voices I've ever heard.