3 awesome videos on very specific topics:
Dr James Grime / Numberphile - Encryption and HUGE numbers http://www.youtube.com/watch?v=M7kEpw1tn50
Les Hazlewood - Designing a Beautiful REST+JSON API http://www.youtube.com/watch?v=5WXYw4J4QOU
classic: Douglas Crockford - JavaScript: The Good Parts http://www.youtube.com/watch?v=hQVTIJBZook