Pragmatic: http://techdistortion.com/podcasts/pragmatic (nothing to do with the defunct Pragmatic Programmers podcast, straight technology talk; professionally produced; replaced Ruby Rogues as my favorite podcast)
Hardcore History: http://www.dancarlin.com/disp.php/hh (when I need to get away from technology and science; professionally produced, no interspersed advertisements)
Seconding Hardcore History by Dan Carlin. I'm currently going through the Blueprint for Armageddon series, where he gives a passionate and compelling telling of the events leading up to and surrounding World War One.
Infinite Monkey Cage: http://www.bbc.co.uk/programmes/b00snr0w (science, brilliant! no interspersed advertisements)
Hardcore History: http://www.dancarlin.com/disp.php/hh (when I need to get away from technology and science; professionally produced, no interspersed advertisements)