Carl Zimmer can really go into detail about the coolest topics in science while remaining clear and easy to understand. I learned a lot about viruses and evolution in this Big Think Interview with Carl Zimmer on YouTube.
Carl Zimmer lecture on evolution and Charles Darwin: Carl Zimmer – Evolution Speaker Series

More videos:

Our Viral Future – Carl Zimmer

A Planet of Viruses – Carl Zimmer

The Origin of Species: 1859 meets 2009 – the evolution of diseases – Carl Zimmer

Many videos are here: Carl Zimmer on Vimeo

YouTube Playlist with all these videos.