Jon Galloway

WordPress feeds offer a choice between Full Text or Summary. The Full Text option is preferable in a lot of cases (e.g. for a podcast), but the feed can grow very large.
One problem with a large feed is that if can exceed the <a href="http://support.google.com/feedburner/bin/answer.py?hl=en&answer=79009" rel="nofollow ugc">Feedburner 512K limit</a>. Your feed may be valid when you first set it up, but eventually when your feed gets big enough, Feedburner will stop updating.
This plugin gives you another setting (available on your Settings / Reading admin page) which sets how many posts should have Full Text. All posts after that will be shown as Summary. This gives you the best of both options – Full Text for new posts, and Summary for older posts. 
<h3>Readme Generator</h3>
This Readme file was generated using <a href='http://sudarmuthu.com/wordpress/wp-readme' rel="nofollow ugc">wp-readme</a>, which generates readme files for WordPress Plugins.

Excerpt Old Posts

This plugin solved my problem with feedbruner.



Greate idea

Shows excerpted content for older posts. This allows more items in the feed while working around the Feedburner 512K feed limit.

S Hetjens

This plug-in redirects requests to the main or comment feeds, and only theses two, to Feedburner or a similar service. In comparision to the original Feedsmith-plug-in is has three advantages:
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It redirects only the two main feeds of the blog and not all. The category, tag and author feeds are still accessible
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If you need access to the original blog feed you can add the URL parameter “noredirect” (i.e. /feed/?noredirect) to your feed address and it will not forward your request.
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The Plugin is more integrated into the administration interface. It adds its settings to the default “reading” settings pages and do not create an own page.
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Hetjens Feed Redirect

This plug-in redirect reqests to the main or comment feed of the blog to Feedburner or a similar service.

Excerpt Old Posts vs Hetjens Feed Redirect