What I've often seen is that the students choose their subject, and then they make an oral presentation to their classmates. The ones I liked best were those that had visual aids. If someone talks about his stamp collection, he brings some stamps to show the students. If someone talks about her new camera, she brings it and explains how to take photos with it. By letting the student decide what will be discussed, he is allowed to use what has been covered already in class, be adventuresome and try new sentence structures, etc. And, of course, the student determines the vocabulary.