Suzanne

For Genesis child themes that output HTML5 only.
This plugin adds an entry field just below the title field on all post, 
page and custom post type edit screens. It allows you to specify a 
subtitle for the content and then outputs the result in an H2 tag just 
under the entry-title where you’d expect to find it.
This plugin is for use with Genesis HTML5 child themes only because it 
uses the hook, genesis_entry_header to position the output after the 
title but before the post-info.

Genesis Subtitles

For Genesis child themes that output HTML5 only.

Fred Dessaint

Epitome Subtitle adds a subtitle field in the edit page of a regular post and static page. Note that a small coding is required to display the subtitle in the right location of your template. You provide to your theme the ability to display a title and a subtitle using functions that you call from your template.
<h4>Functions</h4>
<ul>
<li><code>the_subtitle()</code> takes the current post or page ID and outputs the subtitle.</li>
<li><code>get_the_subtitle($post_id)</code> has one optional parameter (post or page ID) and returns the subtitle as a string.</li>
<li><code>has_post_subtitle($post_id)</code> has one optional parameter (post or page ID) and checks whether a subtitle exists.</li>
</ul>

Epitome Subtitle

Add a subtitle to regular post and static you display with a set of functions from your template.

Genesis Subtitles vs Epitome Subtitle