Kuuak

Simply force display and move the excerpt input box right below the title and before the content.

Excerpt below Title

Move the excerpt metabox below the post title

Andrew Ozz

Excerpt Editor provides a convenient place for creating and editing all excerpts. It can also add custom excerpts for pages (not possible without a plugin). Features: auto-creating excerpts when publishing new Posts and Pages, displaying customisable excerpts from the content for posts without an excerpt, appending excerpts from the latest posts to each Post or from the sub-pages to each Page, replacing the content for all archive and tags pages with excerpts (eliminates content duplication for SEO).
The excerpts can be used in the RSS feed, displayed on the Home or Archive pages and/or used for meta descriptions. The excerpts can be in any language supported by WordPress and the plugin contains .pot file to facilitate translations.

Excerpt Editor

Quick edit or create excerpts for both Posts and Pages, auto-generate and append excerpts or replace the content with excerpts.

Excerpt below Title vs Excerpt Editor