Mostly these are book versions of these plays--the newer ones are still under copyright and won't be available in online free versions. You might find She Stoops to Conquer online (that's a link to the Project Gutenberg version), but mostly you will need to put your hands on the paper versions.
Desire under the Elms by 
A Streetcar Named Desire by 
Arthur Miller's Death of a Salesman by 
The Birthday Party and the Room by 
Angels in America: a Gay Fantasia on National Themes by 
