Someone mentioned Three Days Of Rain, now, I'm not saying it should be done but, seeing as I'm the only one that liked that play...I think it could POSSIBLY work as a musical.
But besides that definitely Miracle Worker, Spoon River Anthology, and The History Boys
Oh, and I have to have my corny say in it...but Chorus Line should never be done as a "musical" but as a play w/ music in it.
wackjack, you are not the only one who liked Three Days of Rain. I saw it the same weekend as I saw History Boys and maybe it was because my expectations were so low for Rain and so high for History Boys, I actually liked Rain a bit better, although I liked both very much. (I think part of my problem with History Boys was that there was an understudy in as Timms and he just didn't work for me--especially since I was reminded of the physical stature of the real actor everytime the video came on). As for Rain, I liked the story, themes, characters and performances very much.
Back to the original theme of the thread: I agree that Rain may work as a musical. I think that the relationships definitely sing.