I think they should make an English version of the book Battle Royale by Koushun Takami. They already made a version, but it is not in English and strays far from the book.
i know they are now but it took them for ever to make a newer movie of the hobbit! and The Historian by Elizabeth Costova is an amazing book and if they dont make it a movie im moving to the moon for good...
Pillars of the earth by ken follet. They already have the sequel (world without end).
My favourite books are G.R.R. Martins "Song of fire and ice" saga, but I like them so much I don't know if I'd like to see them butchered and put on the big screen
The question here is if it should be 'real' movies or animations. Real movies have a hard time keeping up to the plot of the story, and everything stands or falls on the actors. The animation might turn out horrible, as the author might not like it to be all accurate; maybe wanting people to read the book and find the rest of the secrets. Also, many countries have a lot of not-so-good voice actors, who basically ruin everything they try to voice act. In a series, the possibility of new VAs in the different seasons for the minor parts is rather big.