I've always liked the game where you must speak for one minute without repetition, hesitation or deviation. You give the student a topic and they must talk about it for one minute. They cannot veer away from the subject matter. They must not stop to say "um/er" etc but, most importantly they are not allowed to repeat a word (there are a few exceptions to that. They can say "the/a/it/is/I etc" more than once). It's a great way to force students to think of a different way of saying something so if you have all that vocabulary from finished units, broken down into subjects, then you're sorted!
The game is called "Just A Minute" - if you Google it, you will find more info and you can find some clips of the radio/TV versions.
To make sure that all students can get involved, the other students can challenge if they think they have noticed a repetition, deviation or hesitation. If they are correct, the first student has to stop talking and the student who made the challenge carries on speaking about the subject for the remaining time.