Seebz

Improve Page Permalinks. 
This plugin just adds .html to the permalink pages when needed. 
An option can prevent this action for specific pages.
<h4>Example</h4>
<ul>
<li>yourblog.com/page.html</li>
<li>yourblog.com/parent/</li>
<li>yourblog.com/parent/child.html</li>
</ul>
<h4>Compatibility</h4>
Not tested yet with all previous 3.0 WordPress version
Tests OK with the following plugins
<ul>
<li><a href="https://wordpress.org/extend/plugins/permalink-redirect/" rel="ugc">Permalink Redirect</a> (v2.0.4)</li>
<li><a href="https://wordpress.org/extend/plugins/cms-tree-page-view/" rel="ugc">CMS Tree Page View</a> (v0.6)</li>
</ul>

Improved Page Permalinks

Improve page permalinks by adding ".html" for final pages

Mehdi Kabab

When your permalink structure does not end by a trailing slash (/), all your links look like http://example.com/2009/05. Permalink Trailing Slash Fixer add the missing trailing slash.
<h4>Example</h4>
If you have a site with the following permalink structure <code>/%category%/%postname%.html</code> and your permalinks 
look like these:
<ol>
<li>Single Post: <code>http://example.com/my-category/sample-post.html</code>.</li>
<li>Category: <code>http://example.com/my-category</code>.</li>
<li>Archive: <code>http://example.com/2009/05</code>.</li>
<li>Page: <code>http://example.com/about</code>.</li>
</ol>
After activation of the plugin:
<ol>
<li>Single Post: not modified.</li>
<li>Category: <code>http://example.com/my-category/</code>.</li>
<li>Archive: <code>http://example.com/2009/05/</code>.</li>
<li>Page: <code>http://example.com/about/</code>.</li>
</ol>

Permalink Trailing Slash Fixer

Quickly add a trailing slash in the URLs if it's missing in the permalink structure.

Improved Page Permalinks vs Permalink Trailing Slash Fixer