Exit tickets are very common and easy to use for a lesson closure. In this video, we see how a teacher uses the exit tickets to asses his students and help guide his planning. Notice how he moves about the room and talks with his students while they are working. In this way, he gains insight into their thinking, not just their answers.
Watch this video for an outstanding overview of what a closure is, what it can tell you, and how to use it. There are also several helpful strategies discussed. My favorite suggestion is to make sure the students are doing the thinking during a closure, not the teacher.
This article includes a discussion of how to remove hindrances when it comes to closures. The most useful strategy for my classroom has been to set an alarm for when the transition from instruction to closure should begin.
The tactic of using an exit slip is excellent but overused. Here you will find some new ways to close a lesson, including an activity called "What's Inside," where students work with the secret contents of a sealed envelope!
This article explains what a good closure accomplishes. My favorite point is that students start to realize what a closure feels like, and recognize that class is not over until a closure activity has occurred! You will also find some quick ideas for closing a lesson when you are short on time.