Search results - How to return results in Unformatted Text part and Custom Content Parts

Since the Quick Search part is only able to return content results in certain out-of-the-box parts (Formatted Text and Images, Formatted Text and Images (Secured), Discussion Group, Event Calendar, Job Board, and Weblogs), what solution would be best if we want to be able to be able to also search for content inside of “Unformatted Text” parts and Custom Content Parts?