Jerry, I think this is a good thread. Many of the songs I like
have been written for the Broadway stage. Much of this has been
influenced by WS Gilbert, one of the greatest lyricists of all
time.

The reason that the best of these songs work is that they are
tied to characterization (exposition) and deal with imagery
that is unique and brief. Sondheim is the master of this
genre today.

Irving Berlin, Johnny Mercer, Walter Donaldson, Gus Kahn et. al.
have elevated the popular song in America. It would be hard
to find a writer like Mercer or Berlin who can in a few short
phrases capture a memorable image and singeable lyric and melody.
I would place Chris Christopherson, Don McClean, Roger Miller and Rupert Holmes in this higher level of pop song writing too.

John Dowland and Thomas Campion are two of a high water mark
in song writing from Elizabethan England who fused flowing
evocative words with memorable melodies.

A lot of attention is given to the singer/songwriter style of
writing and Stan Rogers, Eric Bogle, Don McClean, Woody, Simon, Dylan etc.and this is OK as far as the style goes. But I believe it would
be helpful for the contemporary singer/songwriter not to
limit his/her horizon to the recent successes but to examine
what makes for a good song regardless of the style.

Much of what is heard in the singer/songwriter genre relies
heavilly on performance style which might not cross over
to other's interpretations.

My favorite songs are those with a soaring melody, a lyric that
expresses 1. specificity 2. a good story 3. a consistency of
form whereby the stanzas are crafted so that there are usually
an equal number of syllables in each line 4. less reliance on telling
(philosophical pronouncements) and more on showing through
unusual and original imagery 5. a tendency to say more using less
words (my folk background here) 6. a rhyme scheme that shows
more effort than laziness 7. an appropriate blending of words
and music and 8. a song that has a life of it's own without being
tied to a specific artist.

Some of my favorites in the singer/songwriter style are:

Band Played Waltzing Mathilda (Eric Bogle)
Vincent (Don McClean)
1913 Massacre (Woody Guthrie)
Pastures of Plenty (Woody)
Mary Ellen Carter (Stan Rogers)
First Christmas Away from Home (Rogers)
Barrett's Privateers (Rogers)
Strange Fruit (Lewis Allen)
Tomorrow Is A Long Time (Dylan)
Four Green Fields (Tommy Makem)
There Were Roses (Tommy Sands)
Black Brown and White Blues (Big Bill Broonzy)
Dark As A Dungeon (Merle Travis)
16 Tons (Merle Travis)
Spanish Is A Loving Tongue (Badger Clark)
Hound Dog Bay At The Moon (Oklahoma college prof.forgot his name)
Trouble in Mind (Richard M. Jones)
How Long Blues (LeRoy Carr)
Dangling Conversation (Paul Simon)
Turn Turn (Pete Seeger)
Old Dan Tucker (Daniel Emmett)
I Wonder As I Wander (John Jacob Niles)
The L and N Don't Stop Here Anymore (Jean Ritchie)
Black Waters (Jean Ritchie)
City of New Orleans (Steve Goodman)
Country Roads (John Denver)
The Pilgrim (Chris Christopherson)
In My Little Cabin (John Jacob Niles)
Ramblin' Boy (Tom Paxton)
Almost all of Tom Lehrer
I'm Changing My Name to Chrysler (Paxton)
The South Coast (Lillian Ross and Sam Eskin)

There are many more I guess but I consider the above to
be masterworks in the singer/songwriter genre.

I believe that most of these songs contain enough of
the 8 elements of good writing that they will survive.

Frank Hamilton