It might be the right time of year to push the use of GeoGebra as a classroom presentation tool. I created this interactive file back in March of this year, and pull it out now with a request for teachers to send in ideas for modifications of this file, or suggestions for new files (send to dave(at)davemath.com. This file can be found here.
Any and all GeoGebra files can be downloaded and modified.
GeoGebra is totally dynamic and its use is limited only by your imagination!