Hmmm... lessee...

Podcasts:
Escape Pod, of course. I also subscribe to Pseudopod and Podcastle, but I'm currently way behind on those eps.
Air Out My Shorts - the drunken college friends I never had. Great for listening to when I can't pay real close attention, like when I'm driving a car.
Nobody's mentioned
Decoder Ring Theatre - they rotate between a few episodes of
Black Jack Justice (hard-boiled detective) and a few of
Adventures of the Red Panda (sorta' Green Hornet-ish wealthy crimefighter), both in the style of Old-Time Radio, but more tongue-in-cheek. During the summer hiatus, expect a few eps of
Deck Gibson - Far Reach Commander (retro sci-fi). Excellent writing and production, great chemistry between recurring characters.
Well-Told Tales - yup.
Surf Guitar 101 podcast - Hey, it's not all litterchur! It originated as a Yahoo! Group and then a discussion forum, for practicioners (sp?) and fans of the Surf, Spy, Spaghetti Western, Instro, and Eleki musical genres. The podcast is a more recent development, featuring a great selection of vintage, 2nd wave, and 3rd wave Surf guitar music (none of that Beach Boys
singing crap though) and interviews with musicians. Your source for twang and reverb. Incidently, it was the
Daikaiju theme music on EP that steered me back to Surf. Made me go out and buy a Fender Stratocaster.
Steampod - I hope he gets this running again on a regular basis. I enjoyed the multi-part
Victoria story.
Dick Dynamo - I tried to enjoy this, but after hearing the first two eps I'm unsubscribing.
The Time Traveller Show Pretty good mix of vintage SF short stories , interviews, and recordings from talks and panel discussions. A few rare gems like a radio interview with H. G. Wells and Orson Welles, together. The feed seems to jump around though, because there are some recent episodes my podcatcher hasn't got.

Podiobooks
Nathan Lowell's "Golden Age of the Solar Clipper" series, beginning with
Quarter Share, and on to
Half Share,
Full Share,
Double Share, and the spin-off story
South Coast. Sorta' Horatio Hornblower meets Honor Harrington, except there's no all-out interstellar war. Find them all in the
Podiobooks.com SF section
Bill deSmedt's
Singularity - I quite enjoyed this, with it's semi-plausible premise. Bit of a hard-SF techno-thriller.
Paul S. Jenkins'
The Plitone Revisionist - Hot babe ... er... plucky heroine overcomes adversity and drags a pair of expositional devices along with her. Owns and operates her own spaceship. Still waiting for the sequel.
Fried Green Zombies - (in progress) Entertaining enough, with good ol'boys, a UFO, zombies (even zombie hotdogs), pickup trucks, dirty cops, mysterious alien babe.
Clear Heart - heartwarming tale of a group of carpenters and such building a large mansion for a dot-com millionaire. Similar sort of appeal as Steinbeck's
Cannery Row, I guess.
How to Succeed in Evil - I enjoyed
HTSIE: Volume One, so I've subscribed to
HTSIE: The Novel

OTR Archived Recordings
There's buried treasure everywhere at archive.org, if you search for
Old Time Radio, with such titles as Sam Spade, X Minus One, CBS Radio Mystery Theater, Lux Radio Theater, Box 13 (hard-boiled), Tales of Tomorrow, Adventures of Philip Marlowe, The Goon Show, (Orson Welles') Mercury Theater On The Air, and pretty much all the usual classic sitcoms, soap operas, variety, big-band concerts, westerns, and adventure series. Some of the entertainment is in the advertising. The older ones tend to have poorer audio, with artifacts from overly-aggressive noise removal.
I find some of the
WWII news broadcasts particularly interesting because it's history being told from a time when
they didn't know how it was going to turn out, which is much different from listening to a documentary. F'rinstance, the big scoop on the D-Day invasion was provided by the German news broadcasts, and not confirmed by any Allied sources, until it was well underway.