Colleague was rhapsodising about the quality of information about plays on the Samuel French website.Take a look here.
Select-a-Play looks fantastic, too. Words from the website:-
Plays to Perform and Play PublishersWe have over two thousand play scripts available for amateur performance, covering all elements of performing theatre: comedy, tragedy, drama, pantomime, sketches, plays with music and full-scale musicals, ranging from classics to new plays, one act plays to full length plays. Use Select-a-Play, our advanced search facility, to help you choose the right one for you. Search by cast, genre, length, period, keyword, title or playwright. Or see our play lists with suggestions for Christmas plays and musicals, pantomimes, plays and musicals for children, schools, youth and student groups.