ajayver

This plugin gives you the ability to change the appearance of your RSS feed. You can easily add images from custom fields, read more link, category list, tag list and any custom code before or after the feed items. Also, the plugin allows you to delay feed publication for several minutes. It is helpful, when you made some mistake and you will have time to fix it before the post went to RSS and all other services like facebook or twitter.

RSS Manager

This plugin gives you the ability to change the appearance of your RSS feed.

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.

RSS Manager vs ReadMore ReadLess