Highlight Comments allows you to highlight comments, which are worth reading. It can highlight your own comments as well and is fully customizable.
After a few authors of blogs wished to have a plugin that enables the ability to highlight some comments on their blog which else wouldn't get the attention they deserve of the readers, I searched one and found 'Comment Hilite'. Unfortunately, this plugin works only with older versions of WP. Later, I explored the plugin 'Highlight Author Comments', which highlights only comments of authors. Highlight Comments is a plugin that combines Comment Hilite and Highlight Author Comments. Its goal is to work on current WP-versions.