During an interview with Ain't It Cool News Louis Leterrier restated his desire to direct The Avengers for Marvel.
"I am on the shortlist, but I'm at the bottom of the shortlist, I'm sure. (Laughs) I don't know who the other guys are, but I have a great relationship with [Marvel], and I've been very vocal to them and everyone else that I am the one to direct it. I loved my time at Marvel. I loved those guys. They're fantastic. Kevin is such a passionate boss; he gets his hands dirty. It's a universe I want to keep exploring. I was frustrated with [THE INCREDIBLE HULK]. It was like, "That's it? Only one superhero? Can I do more???" We'll see. Time will tell."
Seeing as how Jon Favreau has stated that he would not direct The Avengers, I would have to say Letterier is the next best choice.