According to the esteemed Mr. Christopher Nolan, via an interview with the Coventry Telegraph, the third Nolan-Batman movie script has been completed. Nolan himself has stated he keeps his mind firmly planted in one movie at a time, so until Inception is released on July 16th, don't expect too much Batman 3 news. He did however state he is very excited about the story he and his brother Jonathan have in stored. At this point in the Batman process, if Christopher Nolan says he's excited, we should all be excited too.
Source: Coventry Telegraph