MetaX
Automatically generates most of the commonly used meta tags, base tag, and several others.
Revolution Download: http://modx.com/extras/package/metax Revolution Documentation: http://rtfm.modx.com/extras/revo/metax
Evolution Download: http://modx.com/extras/package/metax-evo Evolution Documentation: http://rtfm.modx.com/extras/evo/metax
Author's Site: http://salscode.com/tutorials/2010/07/31/modx-metax