Love podcasts and wrote this list up for g+ a while ago. Many are already mentioned in this thread.
Daily Tech New Show (DTNS) what it sounds like. fun and informative. Hosted by Tom Merritt with guests. It's very well done and keeps getting better.
Bad Voltage - linux stuffs fer the most part, also tech, round table, funny, and definitely the best Linux podcast I've found. Interviews and reviews. Smart without being overly technical
Canadaland - discussion of the media landscape; interviews, opinions.
Hardcore History - Dan Carlin's entertaining, in-depth look at different historical events -I didn't know I liked history before listening to this podcast. Dan Carlin's background is in broadcasting (great voice) and is not a professional historian. Really well produced.
Hacker Public Radio - community driven podcasts on various topics, from hacking the kernel to making a fire.
The SciPhiShow - philosophical discussion using scifi as a touchstone. good discussion. Worth checking if'n ya like scifi and/or philosophy.
Ideas (CBC) -ideas about ideas. arts, science, religion, philosophy, books, ethics, etc. It's hit and miss which episodes I enjoy (just not into all the topics) but when it's good it's great.
The Joe Rogan Experience - Discussion, mostly interview, long form, some GREAT guests from many walks of life, from artists to scientists. I despised 'Fear Factor' and I have little interest in MMA so I thought I wouldn't like this show, but it's great. Rogan is open and real and asks interesting questions. He's a bit open to conspiracy-type ideas but this is more endearing than annoying. Seriously, check this podcast out despite any preconceived ideas you have about it. Joe's a smart cat and he has some incredible guests.
Mission Log: A Roddenberry Start Trek Podcast - best ST podcast out there. ep. by ep. overview, trivia, behind the scenes, discussion of 'messages, morals, meanings' -this is a ST podcast for ST fans -the kind who aren't afraid to hear that some episodes of ST weren't always great.
No Such Thing As A Fish - from the writers of QI (if you don't know the show, it's a long running British TV show that points out interesting facts). Round table, the hosts offer interesting, oft little known facts about...everything.
bathPod Public Lecture Podcast - Long form, lectures from various presenters, 'leaders' in sceince, art, politics. Good stuff; I treat it as a grab-bag.
The Titanium Physicists - a podcast about physics by phycisists; it generally tries to to explain some of the ideas in physics to non-physicists. It's a great show; the only thing I'm not a fan of is the intro which is a take off on Iron Chef -it's fun and al, just not my bag.l
Quirks and Quarks (CBC) -Weekly science news hosted by Bob Macdonald -typically 4 or five science stories and interviews with scientists involved in the stories. Plus everybody's favourite, Q and A shows.
Radiolab (WNYC) most people know of this podcast: stories that often start as science and end with a human story -or vice versa. Great presentation, point of view... wonderful music.
Still Untitled: The Adam Savage Project - Adam Savage and co discussing interesting things: from 'making' to tv, books, cooking, etc. Regular episodes marked as 'spoilercasts' where they discuss movies, and most recently, books. Fun and interesting.
This Week in Tech (TWiT) - round table, indepth discussion of the weeks tech news, hosted by Leo Laporte and various guests from the tech industry or tech media. One of my fave. weekly podcasts. fun. insightful.
Triangulation (TWiT) - long form interview with influential and interesting people in tech and related. Hosted by Laporte it's very well done and he gets some great guests.
Under the Influence (CBC/Pirate Radio & Television) -Terry O'reilly hosts an interesting, informative and fun look at the advertising industry. Something I never thought I'd be interested in.
Welcome to Nightvale - spooky funny irreverent fiction set in the fictional town of Nightvale. presented as 'Community updates'. Think Twin Peaks, Northern Exposure, The Twilight Zone.
Wiretap (CBC) a mix of fiction and non, presented/written by Jonathan Goldstein, a few recurring characters, and interesting guests. erm 'quirky' is an easy way to describe it.
WTF with Marc Maron - long form interview with comedians, artists, actors, etc. Hosted and produced by Maron, a guy who likes cats and whose comedy I like.