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

pyko

A simple plugin that allows you to modify the link that is displayed when you use the <!–more–> feature. Also lets you remove the anchor link to turn off the jumping behaviour. You can also choose to have the more link open in a new window/tab.
You can choose to have just plain text, or also include the post’s title. If you chose to include the title, you can limit the number of characters/words that are displayed in the title. Also allows you to add ellipsis (…) to the title if it has been truncated. All the options can be found in “More Link” tab under “Options” in admin page.

First Post Full Length vs More Link Modifier