One Crayon

If a post is saved with a <code></code> tag that is immediately followed by a common block-level element (like a header, div, paragraph, list, and so forth), then two linebreaks will be placed after the more tag to ensure that the block-level element is not automatically wrapped in paragraph tags by WordPress’ content parser.
There is absolutely no reason to install this plugin unless you are using an external editor and having your whitespace stripped out when you save your posts. If you are editing through the WordPress admin screen, then this plugin will be worthless because you can easily control where the <code></code> tag falls by hand.

Breathable More Tag

Ensure that the  tag has space to breathe if the following tag is block-level

loveless

Provides hooks that can be used within ‘The Loop’ to grab content from before and after the  tag. If no MORE tag is provided, it will return <code>the_excerpt()</code> and <code>the_content()</code> respectively. You can also use a function to access all content, regardless of MORE tag.
<h3>Current version</h3>
Current version: 1.2
<h3>Revision History</h3>
0.1 – made within the functions.php file of the theme 
0.5 – created the plugin, still required $post->post_content to be passed to functions 
1.0 – removed $post->post_content to be passed in. 
1.1 – fixed a bug that stopped <code>the_content()</code> from posting 
1.2 – added function to get all post content, regardless of MORE tag
<h3>GPL</h3>
Copyright 2008 Corey Dutson (email : cdutson@wallofscribbles.com)
This program is free software; you can redistribute it and/or modify 
it under the terms of the GNU General Public License as published by 
the Free Software Foundation; either version 2 of the License, or 
(at your option) any later version.
This program is distributed in the hope that it will be useful, 
but WITHOUT ANY WARRANTY; without even the implied warranty of 
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 
GNU General Public License for more details.
You should have received a copy of the GNU General Public License 
along with this program; if not, write to the Free Software 
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA

PostDivider

Allows the user to select text before and after the MORE tag using custom hooks.

Breathable More Tag vs PostDivider