HHMI’s BioInteractive site has a lot of useful resources including animations.

http://www.hhmi.org/biointeractive/browse?kw=

Their “Image of the Week” newsletter usually includes a great image and story. This week it is about Seeing Single Molecules Move:

http://www.hhmi.org/biointeractive/seeing-single-molecules-move

This could be a great way to explain how transcription factors find their appropriate binding sites on DNA. The animation was produced using real single-molecule tracking data! This resource could be used in a general molecular biology class or even a developmental biology course.