Aaron Sheppard has on-line Reader's Theater scripts that could be used as plays.
http://www.aaronshep.com/
Here are some more online options for upper grades:
http://www.theaterwords.com/plays-for-children.html
http://www.aaronshep.com/rt/RTE.html
http://www.mysterynet.com/short-mystery-classic/
http://youthplays.com/plays.php
http://www.aaronshep.com/
Here are some more online options for upper grades:
http://www.theaterwords.com/plays-for-children.html
http://www.aaronshep.com/rt/RTE.html
http://www.mysterynet.com/short-mystery-classic/
http://youthplays.com/plays.php