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

ramon fincken

Auto sets the more tag to post title if no custom text has been set. 
 Auto text is customizable using mp_auto_more_more_link_readmore filter in the Premium version: 
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Coding by: <a href="https://www.mijnpress.nl" rel="nofollow ugc">MijnPress.nl</a> <a href="https://twitter.com/#!/ramonfincken" rel="nofollow ugc">Twitter profile</a> <a href="https://profiles.wordpress.org/ramon-fincken/" rel="nofollow ugc">More plugins</a>

MP Auto more tag

Auto sets the more tag to post title if no custom text has been set.

First Post Full Length vs MP Auto more tag