I've been told that Conch Key and Sago Cay have really good views of Cinderella's Castle. I plan on requesting Conch Key for our July visit. Check out the GF facts thread at the beginning of the Resorts Page, it really is helpful!
Also, Boca Chica has nice Lagoon Views as well. We stayed at Boca Chica in 99 and had a beautiful view of the Seven Seas Lagoon, Poly and the Contemporary and when looking out to the left of our balcony we had a perfect view of Cinderella's Castle.