Favorite and come back when you need more history

The winner in ratings and awards

The host/writer has a way of dissecting history, adding context and putting it all back together to make a logical whole. Be prepared to follow him deep into a subject as he attempts to explain the reasoning of people and the vagaries of history. He has a way of thinking about subjects that's unique to history podcasts and it's earned him a huge fan base.
The podcast are very long for the genre. A four hour episode about American imperialism in the 19th century is just par for the course. Don't worry though, it's consistently interesting and the time flies as you listen
http://www.dancarlin.com/hh-55/

An aptly named show

This one is ambitious. Starting in 1,000 BC, progressing one decade per half hour episode, it covers all the major civilizations. Given the scale it's no surprise that the show tends to the traditional format of kings and conquerors.
The show is more fun than the short description would suggest. A true fan of history the Host/writer's sense of enjoyment is contagious. At the end of the episodes you can play along with the co-host as he attempts name games such as "Assyrian or Babylonian gods".
http://magicgatheringstrat.com/category/fohcast/

American history with a modern twist.

Three history professors take a subject of current interests and look at it through the lense of history. Each host specializes in a different century; 18th, 19th and 20th. They are often joined by guests to add another take on the subject.
Many of you may know this one already because it's broadcast on radio in 31 states but for everyone else we have the podcast version. If you are a fan of current events and of history this show should be right up your alley. Though, if you're not a Yankee you'll probably want to find a different show.
http://backstoryradio.org/

More than you knew you wanted to know about the crusades

First off, as good as the show is it's told from a Western/Christian historical point of view. Another show that tends to the kings and conquerors model but it does so very thoroughly. Once you've finished a series, such as the First Crusade, you will feel like you have a pretty good understanding of the history of the crusaders.
The host is good at explaining her sources and how they may influence the spin on the story. Subjects that seem particularly interesting often get a dedicated show or short series. This is a very interesting period of history than more than deserves a dedicated show.
http://historyofthecrusades.podomatic.com/

The class clowns turn out to be history nerds

Full of bad puns, silly opening sketches and a general irreverence this show is easily the most fun of the list. The episodes' subjects are pretty wide ranging and you never know what they will be talking about in the next episode. With three years worth of weekly, half hour episodes there's plenty to listen to if you like the show.
You could probably get away with listening to this one on a road trip when the other people aren't history buffs.
http://www.nerdonomy.com/noh/

The podcast that would send Nerds on History to detention for acting up

Here we have the black licorice of the list. Some people love it, some people hate it. Historical crime mysteries? Check. History of popsicles? Check. Episodes about women that are normally footnotes? Check. Hosts that sound like two 14 year old girls doing a class presentation while reading from 3x5 cards? Sigh, check.
This podcast constantly ranks very high in the ratings, and it's been doing so for a very long time, so don't immediately discount it. There are weekly episodes going back to 2009 so there's going to be plenty to interest you in the back catalog. I suggest giving the show a try, you may be pleasantly surprised.
http://www.missedinhistory.com/

This is really a podcast? Cool!

The show's tag line "Historical Myths Relished and Ruined!" gives you an idea of what you are in for here. The concept is to take subjects like the identity of Shakespeare and look at the evidence. This is another unique take on history podcasts.
Our host will remind you of your favorite history teacher, the one that would sidetrack himself and spend half the period off topic, discussing a favorite subject. The show is new, seven episodes so far, but it has quickly gained a good sized fan base. It only took three episodes for me to get hooked on this one.
http://www.ourfakehistory.com/

Let's face it, Limey history has affected us all at some point

Starting pretty much as soon as writing showed up on the isles and going forward in chronological order the show has managed to make it into the 850s AD in a mere 180 episodes, so far. The focus tends towards a holistic view of history so there's a lot that you wouldn't have learned at school. Much more than the retelling of battles and dates.
The host keeps things interesting with a touch of irreverence and a few running gags. Episodes are around twenty minutes each so they are the perfect length for the average commute. Lots to offer here even if you are just slightly interested in British history.
http://www.thebritishhistorypodcast.com/

The new boy on the block

This is a history podcast done by a university professor. The first two episodes cover the Roman slave wars in about four hours. The host/writer is an admitted fan of Dan Carlin's style and it shows.
First time I've seen a history podcast pretty much premier and jump straight to near the top of the ratings. If anything the second episode was better than the first. So far it's off to a promising start.
http://historyonfirepodcast.com/