Classic FM - Discover Music
A good guide to the different musical eras.
What I like about this series is that full of timelines, composer profiles, interesting facts, music examples and most of all it is visually stimulating for students.
The guides can compliment students revision into the various musical eras.
20th Century - http://www.classicfm.com/discover/periods/modern/
Romantic - http://www.classicfm.com/discover/periods/romantic/
Classical - http://www.classicfm.com/discover/periods/classical/
Baroque - http://www.classicfm.com/discover/periods/baroque/
Renaissance - http://www.classicfm.com/discover/periods/renaissance/
Early Music - http://www.classicfm.com/discover/periods/early-music/
This goes with another good video series, possibly as introductions to topics or a summary revision. The Classicfm series highlights the key differences and key composers.