Just wanted to say that I've seen "Buena Sera, Mrs. Campbell" and it's truly awful. Why anyone would want to use it as the basis of a musical book is beyond me.
In the history of musical theatre (at least since Showboat in 1927), nearly every great musical was based on some previous source material -- typically a book or play, or, increasingly since the 60's, a movie. It's much easier to make a list of shows that were totally original, than to make the very long list of shows based on material from another medium.
Some of the totally original shows (not comprehensive):
The Music Man
Bells Are Ringing
How To Succeed In Business (the original book was a joke how-to book and had nothing to do with the story of the musical)
No Strings
Hair
Pippin (has nothing to do with the actual story of Pepin)
Company
Follies
Pacific Overtures
Sunday In The Park With George
Into The Woods (classic characters but the plot's original)
A Chorus Line
Dreamgirls (the Supremes connection is very, very loose)
They're Playing Our Song
Me and My Girl
City of Angels
Falsettos
Hedwig
Urinetown
Avenue Q
"What a story........ everything but the bloodhounds snappin' at her rear end." -- Birdie
[http://margochanning.broadwayworld.com/]
"The Devil Be Hittin' Me" -- Whitney