darrinb

Generates a template tag that allows you to easily display a snapshot of text. 
Useful for meta descriptions, post snippets, or your own custom block of text. 
Displays a snippet of text without having to use the <–!more–> quicktag.

WP Snapshot

Easily display a summary of post text or custom text.

Brijesh Mishra

Show required content and let user click on read more. Visitors will see readmore link on the page, when they will click, rest of the content appear with very simple animation on the same page.
Features
<ul>
<li>This plugin will effect only on pages</li>
<li>Select check box to show read more on the pages</li>
<li>Control option shows on all pages, you can select to show readmore on the page</li>
<li>Define the width to show from the page.</li>
<li>Very simple and easy to use</li>
</ul>

ReadMore ReadLess

ReadMore ReadLess will hide content on page.  Clicking on readmore will show complete page without refreshing the page.

WP Snapshot vs ReadMore ReadLess