Enter redirect from your 404 page
Eliminating Page not found errors (or Error 404) is not as easy as it can be. Recently my Drupal mate osopolar and me created a module which uses the Path redirect module to show it's Add redirect form directly at the Drupal 404 page. As administrator you now can enter the redirect for a not found page without any additional mouse click.
Please check out the module Redirect 404 at osopolar's sandbox and let us know what you think.
Update: There is an Path Redirect issue by osopolar about this too: http://drupal.org/node/1272344