I was just thinking about this the other day.
The Cohen Brothers come to mind, right off the bat. Their adaptations of "No Country for Old Men" and "True Grit" were amazing. I've no doubt they'd capture the Robicheaux saga exquisitely.
Edward Zwick has shown his proficiency with textured storytelling and sweeping epics. (Glory, Legends of the Fall, The Last Samurai)
Frank Darabont does wonders with adaptations. Brilliant writer/director. (Shawshank Redemption, The Green Mile, The Majestic)
David Fincher has a visceral feel to his movies. (Se7en, The Game, Panic Room, Fight Club)
Any crime thriller/drama in the hands of Clint Eastwood is a sure thing. (Midnight in the Garden of Good and Evil, The Mystic) I'm actually surprised he hasn't already opted to do one of the Robicheaux books.
These are my top picks.