Looks Promising…

http://m0n5t3r.info/work/wordpress-plugins/ajax-spell-checker/

http://www.rajprasad.net/plugins/editormonkey/

http://www.lab4games.net/zz85/blog/wordpress-plugins/live-spell-checker/

http://spell.jacuba.com/addit-website.html

http://www.master-technology.com/demos/spell/index.php

http://www.coldforged.org/spelling-checker-plugin-for-wordpress/