This is an update of a post I made a little while ago - if you read that, my new podcasts are marked *NEW* (well, duh). I'd particularly commend the Flammecast (cycling) and Pappy's Flatshare Slamdown (comedy) to you. The Pod Delusion's "Extra" feed is full of gems (Natalie Haynes' talk at the BHA conference, Mark Stevenson's "Optimists Tour of the Future") if you like science, skepticism &c.
Been meaning to do this for a while, but this is a list of the stuff I *try* to catch each episode, or stuff I've enjoyed that's on hiatus but worth subscribing to either for the back catalogue, or a possible new series.
The categories are a bit arbitrary (The Amateur Scientist would fit in Science and Skepticsm too, and Collings and Herrin might possibly fit in news) but do represent what I listen to them for.
Most of the links below go to title pages rather than the RSS itself - I thought this better, as a description for each 'cast would make this a very long post. I subscribe via RSS - I think most of the 'casts have an iTunes feed too, but I can't say for sure as I don't use iTunes.
All the feeds are free, and some have a "tip jar" system for you to donate to the creators if you like the content - others have subscriptions, and some will encourage you to pick up the authors' work or merchandise in other, paid media if you like what they're doing.
Comedy of the Week (Radio 4) *NEW*
Collins and Herring (6 Music Show)
Friday Night Comedy (Radio 4)
Mike Detective (spoof of Pulp Private Eye Stories) *NEW*
No Pressure to Be Funny (NSFW - some bad language) *NEW*
Pappy's Flatshare Slamdown (NSFW - bad language, and depending on who's on it, adult themes) *NEW*
Richard Herring's As It Occurs To Me (NSFW - lots of bad language & adult themes)
The Amateur Scientist (NSFW - occasional bad language & adult themes)
The Collings and Herrin Podcast (NSFW - lots of bad language & adult themes)
What Are You Laughing At? (the British Comedy Guide's new podcast about comedy) *NEW*
What's So Funny? (Another one about comedy, this time from Radio 4 Extra - presented by Rufus Hound) *NEW*
You Look Nice Today (NSFW - occasional bad language & adult themes)
Carrément Vélo (in French)
Cycling Central (Not sure if this one will survive to the next update - like the ITV one, it's a national broadcaster's cast, but unlike the ITV one, seems to assume that people who don't follow cycling will find it all a bit silly - I may just not be getting the humour) *NEW*
Flammecast (occasional bad language) *NEW*
Other Factual (Documentaries, History &c)
Documentary of the Week *NEW*
Music & Film
News & Current Affairs
Global News (Round up of the news of the day from the BBC World Service)
Science and Skepticsm
Monster Talk *NEW*
The Pod Delusion Extra *NEW*
Short Stories and Fiction
Cast Macabre (Short form horror)
Clarkesworld (Short form science fiction)
CrimeWAV (Short form crime and noir on the hardboiled edge of the genre)
Cthulu Podcast *NEW*
Escape Pod (Short science fiction)
Machine of Death (Short Stories about a world in which death (manner, not time) can be predicted. Some really interesting ideas from the different authors) *NEW*
Patrick E. Mclean (Short articles, longer form fiction) *NEW*
Podcastle (Short form fantasy)
Pseudopod (Short form horror)
Scott Sigler Audiobooks (Novel length serialised horror and science fiction, and Scott's reader feedback and interviews elsewhere. Definitely not for kids. The current serial is "Ancestor", but Scott's back catalogue is available too, including fan favourites like "Contagious" and "Earthcore")
Shadow Publications (Author Paul Elard Cooley's Feed - short and long form horror fiction) *NEW*
Toothless (Novel length serialised horror - an interesting twist on the zombie genre so far - not for kids).
Underwood and Flinch (Mike Bennett's novel length serial tale of a vampire and his reluctant servant in modern day Spain - again, not for kids)
(Also worthy of mention is the MIGHTY podiobooks.com, which has more serialised audio fiction than you can shake several sticks at, and an excellent personalised subscription system).
It's worth noting that the biases of the Internet mean that much of this is horror, fantasy and science fiction - and lots of it is written specifically to be somewhat disturbing (it's horror, after all!). As I recall, Clarkesworld, Escape Pod & Podcastle will give a guidance rating with stories, so should be safe for those of a nervous disposition (as long as you pay attention to it).