Science and comedy, fits your brief perfectly and is very careful not to take itself too seriously.

This is a new one I found, an American bloke is telling the story of the UK from the Ice Age to modern times. He's only as far as Hadrian's Wall but it's very good.

http://itunes.apple.com/gb/podcast/the-british-history-podcast/id4409853...

Also David Hepworth of this here parish posted a link to a very fine podcast of old time country music which is just fabulous.

http://itunes.apple.com/gb/podcast/joe-bussards-country-classics/id35740...

Stuff you should know
This American Life
Skeptics Guide to the Universe
Sound Opinions

This American Life for compelling story-telling, and WNYC's Radiolab, for a thought-provoking, accessible and interesting slant on science. Both are funny, too.

Stuff You Should Know.

How Stuff Works also do a set of Technology ones which take an aspect of technology and make sense of it for the rest of us. I enjoy these ones a lot.

Listen to Lucy (business world polemic from Lucy Kellaway of the FT)
A History of the World in 100 Objects (download the lot, Radio 4)
Old episodes of In Our Time with Melvyn Bragg, Radio 4
Some of Peter Day's World of Business can be pretty absorbing, Radio 4 (two strands, GlobalBiz and InBiz)

Desert Island Discs - now around 10 years of archives available - some more interesting than others.

And for something a little more thought provoking : In Our Time , 3 experts discussing a subject - I can't admit to always understanding everything but you can't fail to be impressed by the immense knowledge of the contributors.

Mayo & Kermode

Trevor Danne radio academy

Desrt island discs

Predictable I know, but I like them.

I know Richard Herring has appeared on every podcast list on this forum but his latest one, a daily podcast with a different (comedy) guest everyday is very good (after an understandably slow start). You do have to like RH though.

I'd recommend The Age of Persuasion, where Host Terry O'Reilly "explores the countless ways marketers permeate your life, from media, art, and language, to politics, religion, and fashion," as per the website.

O'Reilly, an experienced ad man, is so thoroughly enamored of his field, he employs the best and most insinuating tricks of his trade to unveil the curtain. It sounds like nothing else on Canadian public (and non-public) radio, and a number of episodes are available for download on the program's site http://www.cbc.ca/ageofpersuasion/

No-one's mentioned it, so I'd go for the Bugle - silly political humour. The best British podcast, in my opinion.

If you like your humour scatalogical, Hollywood Babble-On is fantastic.

And if you like your humour angry and ranty, The Adam Carolla Show is great stuff.

Hardcore history.
Europe From It's Origins,
A History Of WWII.
AIOTM! (AIOTM!).
TV Cream.
Watching The Directors.
Guardian Football Weekly.(and Exxtraa!)

And, if you like puerile cock gags...

Hollywood Babble-on
and
Jay And Silent Bob Get Old

oh...
There's this thing called The Word Podcast too with two blokes from out of Smash Hits when it was the best bi-weekly mag evah!!!