I love giving the students a problem to solve or a "ticket out the door." Not only is it motivational and gets them working, it is a great way to assess learning in a quick way. I put a problem or question on the board, and the kiddos answer on a 3 x 3 sticky note. On the way out, they place the sticky on their corresponding number. Also a quick way for me to check who completed the problem as well.
Check out my blog for details on how I made my poster: