Nima Arkani-Hamed is an amazing speaker, and if you're interested in modern physics I highly recommend watching his talks. A great place to start is his 5 part Messenger lecture series. It starts with the discovery of quantum mechanics, and the last 3 talks all cover different frontiers of fundamental physics today.

http://www.cornell.edu/video/playlist/nima-arkani-hamed-on-f...

Introduction ends and Nima starts about 4 minutes into the first lecture. :)