Jonathan Brinley

The standard excerpt field will appear on pages, just as it does on posts.
Additionally, there is a new widget to display the excerpt of a selected page.
Created by <a href="http://flightless.us/" rel="nofollow ugc">Flightless</a>

Page Excerpts

The plugin is built for something very specific, and does it perfectly.

Simple but effective

Adds an excerpt field to pages, and provides a widget for displaying page excerpts

Stephanie Leary

Creates widgets that display excerpts from posts or pages in the sidebar. You may use ‘more’ links and/or link the widget title to the post or page. Requires <a href="http://blog.ftwr.co.uk/wordpress/page-excerpt/" rel="nofollow ugc">Page Excerpt</a> or <a href="http://www.laptoptips.ca/projects/wordpress-excerpt-editor/" rel="nofollow ugc">Excerpt Editor</a> for page excerpts. Supports <a href="http://robsnotebook.com/the-excerpt-reloaded/" rel="nofollow ugc">the_excerpt Reloaded</a> and <a href="http://sparepencil.com/code/advanced-excerpt/" rel="nofollow ugc">Advanced Excerpt</a>.
Now on <a href="https://github.com/sillybean/Post-and-Page-Excerpt-Widgets" rel="nofollow ugc">GitHub</a>.

Post and Page Excerpt Widgets

Creates widgets that display excerpts from posts or pages in the sidebar.

Page Excerpts vs Post and Page Excerpt Widgets