Here's a new AJAX Enabled Dropdown action from user petasis. He's adapted the Dynamic Dropdown action to allow you to return any valid HTML and insert it into a tag on your page (typically a div but it could be any tag).
Note: This action is for ChronoForms v4 only; it should work with both the Joomla! 1.5 and 1.6 versions.
To install this action please upgrade to ChronoForms v4 RC3,0 and use the Action Installer icon in the Forms Manager toolbar.