I like the speed quiz game. You split the class into two teams, and have one student from each team face away from the screen. Show a picture of an activity on the powerpoint (ex: someone riding a bicycle). The teams must act out the action without speaking (keeping noise levels down), and the two students must make a complete sentence (You are riding a bicycle). The first student to form a complete sentence wins a point for their team.
If students are having trouble, you can allow their teams to speak, but then the noise levels increase.