WordPress plugin that allows the marking of the new comments in a post.
When an user visits a post in your blog the plugin registers the time of the visit in a simple cookie. This allows that when the user comes back to the post searching for new comments these could be marked.
To do so the plugin adds the 'unread' CSS class to the comment. You will only have to customize that 'unread' class to mark new comments.
This plugin uses some code from: Brett Taylor (http://inner.geek.nz/archives/2005/02/11/wordpress-plugin-smart-unread-comments/) Utkarsh Kukreti (http://wordpress.org/extend/plugins/feature-comments/)