Bernhard Kau

This plugin will show the first post with its full text but all the others with the text after the “more” tag

First Post Full Length

This plugin will show the first post with its full text but all the others with the text after the "more" tag

fabio.mazzarino

In-Post Template plugin add additional content to posts and pages, inside the_content() data result. It can be used to add sitewide content like AdSense, banners and plugins.
It accepts to insert html, java script, embedded content, php and even others plugins. Template tags are also accepted.
It replaces a special mark added inside the post which can be the  mark or any other configured.

In-post Template

In-Post Template plugin add additional content to posts and pages, inside the_content() data result.

First Post Full Length vs In-post Template