There is a surviving episode of "Eye Witness" from 26 February 1948certainly one of the earliest existing example of U.S. television content!
Though lost now, how about the 1947 BBC production of the play "Rope", a year before the Hitchcock film? Sounds like it could have been a classic. If those original transmission signals are still travelling through space, I hope they recover them some day.
"That coaxial cable looks sensational" - "Oh thank you Harry, but that's stuffed celery"

Toast of the Town, Talent Scouts, The Original Amateur Hour, The Gay Nineties Review,
and
The Ed Wynn Show
were mentioned above. I'll add:
Hour Glass
(1946-47),
Cavalcade of Stars, Let There Be Stars, Hollywood On Television, Broadway to Hollywood, The Eyes Have It / Celebrity Time, Doorway to Fame, Hollywood Screen Test, Front Row Center, Places Please, The School House, Musical Merry-Go-Round, Inside USA With Chevrolet, Uptown Jubilee, The Little Revue, Buzzy Wuzzy
(which lasted less than a month),
America Song,
and
Memory Lane.
Faraway Hill
(1946) was "the first soap opera broadcast on an American television network" according to Wikipedia. Later (1949) TV soaps include
These Are My Children, A Woman to Remember,
and (as mentioned)
One Man's Family
(which started on radio in 1932).
Hopalong Cassidy
(1949) was the first network TV western series.
The Lone Ranger
TV series premiered later that year, the first western series produced specifically for television.
Crusade in Europe
(1949) was the "first extensive documentary series for television" according to Wikipedia.
The Voice of Firestone Televues
(1943-47) presented various documentary shorts.
The World in Your Home
(1944-48) and
Serving Through Science
(1946-47) were early educational shows.
Eye Witness
(1947-48) was a documentary series
about
television (not to be confused with a 1953 series of the same title).
The world's first TV game show was
Spelling Bee
(UK) in 1938. In 1941, an experimental airing of
Truth or Consequences
was the first appearance of a game show on US TV.
CBS Television Quiz
premiered the following night. Other US game shows included
Cash and Carry
(1946-47),
Pantomime Quiz
(predecessor of
Stump the Stars
),
Charade Quiz, Face to Face, Americana, Quiz Kids, Campus Hoopla,
and
Okay, Mother.
According to Wikipedia,
Public Prosecutor
first aired in 1951, but filming began in 1947, the earliest filming of a US TV drama series. The first broadcast of a filmed US drama series was
Your Show Time
in 1949.
Bobmck mentioned
Captain Video and His Rangers.
Opryphantom mentioned
Kukla, Fran and Ollie.
I'll add:
Howdy Doody, The Adventures of Oky Doky,
and
Lucky Pup / Foodini the Great.
Bobmck mentioned
The Philco Television Playhouse.
I'll add:
Kraft Television Theatre, Ford Theatre, The Chevrolet Tele-Theatre, Colgate Theater, The Silver Theater, Fireside Theater, Program Playhouse, Television Playhouse, Actor's Studio, ABC Television Players
(a.k.a.
ABC Tele-Players, ABC Penthouse Players
), and
Texaco Star Theater
(Opryphantom mentioned "Uncle Miltie," the nickname Milton Berle introduced on that show).
Bobmck mentioned
Hands of Murder.
I'll add:
Suspense, The Plainclothesman, They Stand Accused, Your Witness, Chicagoland Mystery Players, Man Against Crime
(a.k.a.
Follow That Man
),
DuMont Mystery Theater
(not listed on IMDb),
Starring Boris Karloff
(a.k.a.
The Boris Karloff Mystery Playhouse
), and
Martin Kane, Private Eye.
Mary Kay and Johnny
(1947-50),
Mama, The Aldrich Family, The Goldbergs, The Growing Paynes, The Morey Amsterdam Show, The Life of Riley,
and
Pinwright's Progress
(UK) have all been mentioned. I'll add:
The O'Neills, The Laytons,
and
The Ruggles.
Lastly, I'll mention the
Oboler Comedy Theater,
and (I almost forgot)
Ruthie on the Telephone.
(Apologies for omissions and any errors.)

There were mini-series and feature-length one-off plays in the UK, but these are lost. Shame really.
As already noted the US anthology series of the era presented one-off plays that were similar to TV movies except performed live.
I read about a Soviet mini-series from the 1930s (yes, 19
30s
) which may have been filmed instead of live, wonder if that still exists.
Here is the link (IMDb lists it as a film):
http://www.imdb.com/board/10029726/
"That coaxial cable looks sensational" - "Oh thank you Harry, but that's stuffed celery"

<<
tv mini-series didn't start until sometime in the 1970's decade.
at leasr in the U.S.
although I guess technically, you could sort of count some episodes of Disneyland (The Wonderful world of Disney/Disney's Womderful World Of Color) as mini-series, such as Davy Crockett and some others, though that was in the 1950's, not the 1960's
But technically, that wasn't a mini-series either since Disneyland was a regular weekly show.

BTW, currently Hulu has those same 17 episodes of
Studio One
.
http://www.hulu.com/studio-one
http://www.hulu.com/grid/studio-one?video_type=episode
(Click "ALL" in the season selector on that page.)

It is a very interesting collection :
Includes 17 restored ""STUDIO ONE"" Dramas:
"1984" (original broadcast: September 21, 1953)
"An Almanac of Liberty" (original broadcast: November 8, 1954)
"The Arena" (original broadcast: April 8, 1956)
"Confessions of a Nervous Man" (original broadcast: November 30, 1953)
"Dark Possession" (original broadcast: February 15, 1954)
"The Death and Life of Larry Benson" (original broadcast: May 31, 1954)
"Dino" (original broadcast: January 2, 1956)
"Julius Caesar" (original broadcast: August 1, 1955)
"June Moon" (original broadcast: June 22, 1949)
"The Medium" (original broadcast: December 12, 1948)
"Pontius Pilate" (original broadcast: April 7, 1952)
"The Remarkable Incident at Carson Corners" (original broadcast: January 11, 1954)
"The Storm" (original broadcast: October 17, 1949)
"The Strike" (original broadcast: June 7, 1954)
"Summer Pavilion" (original broadcast: May 2, 1955)
"Twelve Angry Men" (original broadcast: September 26, 1954)
"Wuthering Heights" (original broadcast: October 30, 1950)
I have no doubt that Mr. Menotti is well respected. I had just never seen a dramatic piece like that where everyone sings their dialog.
A friend of mine and I when we were kids did a tape recorded version of the TV show SWAT but all the cops sang everything.
I have seen people sing on silly things like "Cop Rock" & "Hull High" 20 years ago.
HaPpIpUPpI 13 Arf!

"The Medium" is a Gian-Carlo Menotti opera which is still performed by repertory companies today. Menotti is a very respected composer who started the yearly Spoleto music festivals in both Italy and the U.S. His "Amahl and the Night Visitors" was commissioned for a Christmas television broadcast and is familiar to many schools and theaters as an annual holiday treat. Your report makes that vintage Studio One collection sound (no pun intended) interesting.

I just checked out a DVD Box Set from the library of CBS "Studio One" that dates back to the Fall of 1948.
The episodes were not "filmed" but recorded in Kinescope style. (Putting a big camera to the TV screen and "filming" it that way. ) Good thing too or all these shows would be lost for good.
The very first show is not on the DVD set.
. but the oldest one and first on DVD #1 is from Dec. 12th,1948. It's a one hour "operetta/modern opera" called "The Medium".
"The Medium" is an old fashioned term for a Psychic or fortune teller. In the show the actors actually "sing" every bit of their dialouge. (A lot of it doesnt rhyme but I don't think it was meant to.)
Their dialouge,like talking,tells the story. I couldn't help but laugh at some of this. The "fake" fortune teller invites 3 people to have a saence and contect their long lost loved ones. I wont describe the whole plot but I was finallt able to stop laughing and watch the rest.
The rest (from what I read on the box) are straight acted.
It even came with the original "station identification announcements".
"You're Watching CBS" etc. then the local TV station would give it's call letters (example only "this is WCBS out of New York").
HaPpIpUPpI 13 Arf!

Probably correct, though I guess you could say those TV anthology series were like very short TV movies.
"It's Bucket 'o Nothing! Surprise your friends, amaze your family, annoy perfect strangers!"

Any good made for TV teledramas or miniseries?
No made-for-television movies back in the 1940s, nor any television mini-series.

I don't recall anything that could be classified a miniseries, but
in the categories of either Drama or Comedy:
"Mama"
"The Goldbergs"
"The Aldrich Family"
"One Man's Family"
"Candid Camera"
"The Philco Television Playhouse"
"Hands of Murder"
Variety:
"Toast of the Town"
"Talent Scouts"
"Ted Mack's Original Amateur Hour"
Sports:
"Gillette Cavalcade of Sports"
Adventure:
"Captain Video and His Video Rangers"
"The Lone Ranger"
Culture:
"Voice of Firestone"
Long-lasting:
"Meet the Press"

Uh, no. Most early TV stars came from Radio, the stage and in some cases from Jewish Nightclubs (or something along those lines).
"I Love Lucy" wasn't the first sitcom to have a pregnant chartacter. That was "Mary Kay and Johnny" in 1948 (like "I Love Lucy", Mary was pregant in real life and they decided to include this into the show).
"It's Bucket 'o Nothing! Surprise your friends, amaze your family, annoy perfect strangers!"

Interesting. I suppose the 1950s I Love Lucy was more socially daring than these earlier models, insofar as she was married to a Cuban man and was even shown pregnant.
Were the earliest television stars Hollywood B-listers who latched onto a new medium? Was there a stigma associated with television acting as opposed to film acting?

In response to sitcoms: 1940s TV sitcoms included "Mary Kay and Johnny" (1947-1950, with a premise similar to 50s sitcoms like "I Love Lucy", "I Married Joan", etc), "The Growing Paynes" (1948-1949), and "Pinwright's Progress" (1946-1947)
"It's Bucket 'o Nothing! Surprise your friends, amaze your family, annoy perfect strangers!"

No, but Uncle Miltie and KUKLA FRAN and OLLIE, started in late forties.

The show may be dated, but he was a tremendous talent. His work on The Twilight Zone was exquisite.

"The Morey Amsterdam Show" was and still is a pretty good sketch-comedy/sitcom hybrid..
"The Gay Nineties Revue" was among the better shows on what would one day be ABC.
"The Life of Riley" with Jackie Gleason is pretty good.
"The Ed Wynn Show" is rather dated but is fun.
"Public Prosecutor" is very low budget but still a good crime-drama.
"It's Bucket 'o Nothing! Surprise your friends, amaze your family, annoy perfect strangers!"