This is Brian Pankuch's idea that I heard of during a PDC meeting, but it was so good I had to share it.

Hand out 4 color index cards, one of each color, per student.  Then throughout the lecture to see if the students are getting it ask questions that can be answered either true or false, red or blue or multiple choice yellow is a, green is B, red is c and blue is d. 

This gives feedback to the instructor if the students are "getting it" and it forces the students to participate.   Another everyone wins idea!