Jeesh - I wish I could remember the time frame, but I did a whole thread on cake! My favorite is white wedding cake, and I asked the same question you did! I mean, chocolate's okay, but bring me the white cake!!!
I love the ginger cake at Yakatori, which isn't white, but still is very light and airy! Chef's de France had a wonderful peice of white cake with chunks of real strawberries.
I also shared my recipe for chite cake and white frosting that I've had to perfect over time, to compensate for the lack of a good white cake!
Good luck with your quest! Keep us posted if you find any outstanding cake.
Oh - I plan on trying Fountainview over in Epcot, supposed to have great cake of the day, but it's not always open.