Visualizing the Diffie-Hellman key exchange
If you just want to watch so the video, here you go. But this article also contains some more information below.
In 2010 I blogged about Khan Academy featuring free video lectures. Seems like the site is growing quite well with topics covering a large spectrum of science.
One of the most interesting video series I found there was Journey into Cryptography
It offers a great oversight of encryption methods, historical relevance and most importantly, emerging patterns that offer an attack vector due to lack of entropy which leads to a low key-strength. This video is a great way to get into the principles of cryptography.
The series can also be watch directly on youtube via this playlist: