WordPress.org

Unlike more complex plugins for managing redirects, the Redirect Editor gives you a simple textarea to edit and manage .htaccess-style 301 redirects, one per line.

Enter each redirect rule in the following format, starting with the relative path of the URL to match, followed by the absolute URL of the destination to redirect to, separated by a space. Each redirect should be on its own line. Blank lines and lines that start with # (hash) are ignored and can be used for spacing and comments.

/2012/09/old-post/ http://www.example.com/2012/09/new-post/

After installing, go to Settings > Redirect Editor to configure.

If you're interested in contributing to the code behind this plugin, it's also hosted on GitHub: https://github.com/justincwatt/wp-redirect-editor