Some of the young adult backlist for the classic books have been making publishers money for decades. (deanwesleysmith.com)
Ebooks work on a «pay on scan» model, effectively, but in some cases that would actually get publishers their money faster than the lengthy payment times some accounts take. (blackplasticglasses.com)
Short, single items do not make publishers money (they can't charge enough for a public that wants value), so agents will not represent it.Your best bet for short works are journals and magazines. (matthew-iden.com)