I agree with Brandon Sanderson's stuff, David Gemmell (the man wrote so much fantasy it's frankly astonishing none of it's been picked up yet) or the Night Angel... Mortal Engines would be nice too... but I think I'd really like the Dice Man by Luke Rhinehart, or perhaps Sabriel by Garth Nix, to be made into films or games... I think they'd both work as games, Dice Man's 'dicelife' system could be fun. And as to the poster above who said 'Halo: The Flood' should be made into a game, wasn't that a novelization of Halo? A game?
I may simply have missed the joke there.