According to AllThingsD:

Tuesday, Oct. 4.

That’s the day Apple is currently expected to hold its next big media event, according to sources close to the situation, where the tech giant will unveil the next iteration of its popular iPhone.

AllThingsD also states that Apples new CEO Tim Cook will be the one leading the keynote speech at this, and all future, Apple events. I think that is not necessarily correct. Cook will likely lead this one to show everyone that he really is the new man in charge. However in the future someone else might be better qualified to do the keynotes. To paraphrase John Gruber, Steve Jobs didn’t do the keynotes because he was the CEO. He just happened to be both the CEO and a really great keynote speaker.