Here I list some further radio series, both old and new, which may be of interest to those new to the world of audio drama, along with a bit of background on each. Some of the series listed below may be 'upgraded' to their own page on the Plot Spot down the road.

2000 X (2000)
Produced by the Hollywood Theater of the Ear for NPR as part of a millennial celebration, this anthology of SF dramas featured Harlan Ellison as host and several renowned actors in the title roles.  Episodes varied in length from 3 minutes to almost an hour. Info on purchasing is available at Audible.com and Amazon.com. 

The Adventurer's Club (1933)
also known as Strange Adventures in a Strange Land, this series of 15 minute adventures  derived its material from supposedly true stories, told in the format of a meeting at a club of - you guessed it - adventurers. 37 episodes.

The Adventurer's Club (1947-48)
Unrelated to the above mentioned series except in  title, this was a childrens' series of half-hour adventures. 14 episodes.

Alien Voices
A current series which is actually a collaboration between Star Trek's Leonard Nimoy and John deLancie (Q), Alien Voices commercially releases classic works of science fiction, semi-dramatized - that is, readings with varying amounts of added sound effects, actors, and music. So far they have produced modern versions of several stories by Jules Verne and H. G. Wells, such as The Time Machine, The Invisible Man, First Men in the Moon, War of the Worlds, and Journey to the Center of the Earth. Can be purchased at most bookstores.

Alien Worlds (1979)
A 'character' series - that is, a series with a set of standard characters as opposed to an anthology of unrelated stories - about an orbiting space station called StarLab and the strange cosmic mysteries encountered by its crew. 30 episodes were produced, some  penned by Joe Stracinsky, the creator of Babylon 5. More info and CDs or tapes can be found at the official website: http://www.alienworlds.com/default.htm

Arch Oboler's Plays (1939-40; 1964)
see the 'Lights Out' archive.

Beyond Tomorrow (1950)
see the 'Miscellaneous Shows' archive.

Captain Starr of Space (1953-54)
A juvenile serial, in the same vein as Space Patrol and Tom Corbett. Only about a half dozen episodes survive.

CBS Radio Workshop
see the 'Miscellaneous Shows' archive.

Columbia Workshop (1936 - 47)
An early anthology series that experimented with unique approaches to telling its stories, and dealt in multiple genres. Ventures into  SF and Horror included versions of The Tell-Tale Heart, The Signalman, R.U.R. (Rossum's Universal Robots), The Horla, and Metzengerstein. See the 'Miscellaneous Shows' archive for further episode info.

The Creaking Door (196?)
Another South African series, an anthology of horror and crime stories. Most episodes were derived from the Inner Sanctum series.  At least 34 episodes were produced.

Creeps By Night (1944)
Murder and Occult stories. 16 episodes were produced, including two with Boris Karloff, The Final Reckoning and The Hunt. Only about six of the episodes survive.

Dark Fantasy (1941-42)
28 of 31 episodes still survive of this local series out of Oklahoma City, which spanned the gamut of stories from murder tales to SF and horror. The show had a tie-in with Movie Radio Guide, which printed the stories along with illustrations. 

Darkness (1979)
A local series out of Long Beach, CA produced for National Public Radio. Between 10 and 13 episodes were made, all horror. See the 'Miscellaneous Shows' archive.

The Devil and Mr. O (1971-72)
see the 'Lights out' archive.

Doctor Who (1976--  )
As enduring as Star Trek, the British TV series ran for 3 decades, with numerous incarnations of the famous Doctor.  The BBC produced -as far as I can figure - about half a dozen radio dramas based on the series, starring whatever actor was the current Doctor, from 1976 up to 1999. There are also well over a hundred shows made by various independent producers licensed by the BBC. 

Family Theater
see the 'Miscellaneous Shows' archive.

Favorite Story (1946-48)
This series produced shows from all genres, pulling its ideas from selections of various celebrities choices for their personal favorites. About 18 episodes could be called SF or Horror, including adaptations of Frankenstein,  The Monkey's Paw,  The Time Machine, and 20,000 Leagues Under the Sea.  All were half hour shows. See the 'Miscellaneous Shows' archive.

Fear on Four (1988-1993; 1997)
An intermittently produced series for BBC 4, multi-genre in nature, covering crime, horror, and SF. Very high quality production values and solid acting; 47 episodes, including version of The Monkey's Paw and The Yellow Wallpaper. Some episodes are included in the 'BBC' Plot Archive

Flash Gordon (1935-36)
A very dated serial based on the famous pulp character, only the first half of the serial survives to this day. Episodes were cheaply produced and short - only 15 minutes each.

The Inner Sanctum (1941-52)
One of the most famous radio series ever done, Inner Sanctum dealt mostly with murder stories, but occasionally ventured into the horror genre as well. Although it remains uncertain just how many episodes were made, there appears to have been more than 140, all in half-hour format.  A separate series of the same name was produced in Australia.

Johnny Chase, Secret Agent of Space (1978-79, '81)
A CBC comedy serial spoof of  space operas, this series followed the adventures of a bumbling hero and an assorted cast of misfits, including a self-important wisecracking computer, a psychic and a trigger-happy ex-soldier, as they ran afoul of cliche space villains intent on destroying Earth. The show ran for two seasons. 

Journey into Space (1953-56)
Perhaps the most successful and popular series to come out of Britain. The three separate serials  made followed the exploits of astronauts exploring the Moon and Mars who uncover an alien plot to conquer Earth. The show was enough of a hit to inspire fan clubs and retrospective documentaries.

Lux Radio Theater
see the 'Miscellaneous Shows' archive.

Macabre (1961-?)
A production of Armed Forces Radio, this series was produced somewhere in the South Pacific for servicemen overseas. See the 'Miscellaneous Shows' archive for further episode info.

Mercury Theater on the Air
see the 'Miscellaneous Shows' archive.

Murder at Midnight
see the 'Miscellaneous Shows' archive.

Mystery in the Air (1947)
A short-lived horror series hosted by Peter Lorre of 13 episodes, only 8 of which are still extant. Among the surviving episodes are renditions of The Horla and The Marvelous Barrastro. See the 'Miscellaneous Shows' archive for further episode info.

NBC Presents: Short Story 
see the 'Miscellaneous Shows' archive.

OMNI Audio Experience
see the 'Miscellaneous Shows' archive.

The Planet Man (1950)
Intolerably cheesy kids' space opera serial of 15 minute episodes, cheaply produced with appropriately unbearable organ accompaniment.  78 shows.

Radio City Playhouse (1948-50)
A half-hour multi-genre anthology series which featured about a half dozen stories of the fantastic, among which were adaptations of How Love Came to Professor Guildea and Ray Bradbury's The Wind. See the 'Miscellaneous Shows' archive for further episode info.

Sleep No More  (1956-57)
A short-lived series of readings by Nelson Armstead, primarily focusing on horror. The shows were in half-hour format, though often included two stories per episode.

Strange (1955)
A short series of 15 minute adaptations of horror stories. Only 4 episodes are known.

Tales of Tomorrow
see the 'Miscellaneous Shows' archive.

Theater Guild on the Air
see the 'Miscellaneous Shows' archive.

The Strange Dr. Weird (1944-45)
A spinoff series of The Mysterious Traveler, our good doctor spun new spins on stories from its parent series, condensed to 15 minutes from the original half-hour. Its sister show, The Sealed Book, derived its stories from MT's murder mysteries, while Dr. Weird lived up to his name and dealt with the supernatural. Maurice Tarplin, the host of MT, also emcee'd this show. 28 episodes.

Theater 10:30 (197?)
A CBC multi-genre anthology series which focused mainly on SF and horror. Its more prestigious offerings included The Monkey's Paw and a 2-part adaptation of Ray Bradbury's Dandelion Wine. See the 'Miscellaneous Shows' archive for further episode info.

Tom Corbett, Space Cadet (1952)
This rockets 'n ray guns kids' show could vie with Planet Man as perhaps the cheesiest space opera in the annals of radio. It shared the same unbearable organ accompaniment and, like its contemporary rival Space Patrol, its presence on the radio was a spin-off from a  television series (though IMHO it lagged behind SP in almost every respect).  Each storyline was presented in two 15 minute episodes.

The Vanishing Point
see the 'Miscellaneous Shows' archive.

The Weird Circle (1946-47)
A series which properly cannot be labeled as a horror show, as  it dealt for the most part with stories which only used a supernatural element as a red herring to cover an ultimately mundane and all too earthly explanation for the weird goings-on.  There were exceptions of course, including productions of The Oblong Box, The Thing in the Tunnel, and Dr. Jekyll and Mr. Hyde. 78 episodes were produced in half-hour format.  See the 'Miscellaneous Shows' archive for further episode info.

The Witch's Tale (1931-38)
A seminal series which established the standard of a  host-based anthology series, and the first horror series produced for radio. Exact numbers are difficult to nail down, but there were likely in the neighborhood of 150 stories produced, some in 2 or 3 parts, all of them original to the series. About fifty of the shows were remade in Australia and broadcast there in probably 1949-50.