Chronological:

• Ray Harris Jr.- The History of World War 2
• Mike Dunkan - The History of Rome
• Robin Pierson - The History of Byzantium (follow up podcast)
• Khodadad Rezakhani - Iranologie (History of Iran)
• The British History Podcast

Other:

• The AskHistorians Podcast (Intervies with AskHistorians contributers)
• New Books in History (Interview with Authers)
• Dan Carlin - Hardcore History
• Russ Roberts - Econtalk (mostly about Economics but includes quite a bit of History)

There are more, but others I have either not jet listen too, or I don't think they are quite as good as the ones I have named.

Edit: Maybe not really a podcast but you might still like it. The youtube channel "TheGreatWar" goes threw the First World War week by week tracking the original war 100 years later.

In Our Time is a radio program that covers a whole host of topics, history included. I love it.

For what it's worth, I've listoned to Pierson's history of Byzantium and thought it was rather poor and that he makes a number of assumptions that I would strongly disagree with.

Edit: it's podcasted.

Greg Proops, Smartest Man in the World :). While not about history per say, he likes to pepper his podcasts with multiple historical examples, stories, figures, etc. I wouldn't take everything as gospel truth, but boy, does it ever make a long drive go fast.

Also, I am mildly amused by The Bowery Boys, NYC history podcast.