Brian Zeligson

WP Custom Taglines adds a meta box to your posts and pages with two options, Enable Custom Tagline, and Custom Tagline Content. Checking 
“Enable Custom Tagline” will cause your site to display the contents of the “Custom Tagline Contents” field on your site when that post or 
page is viewed, instead of the sitewide tagline.
Check out http://www.workinginboxershorts.com for more plugins, for support or questions, or to contribute code.

Custom Taglines

WP Custom Taglines allows you to specify a custom tagline for each post or page that will override the sitewide tagline for that post or page.

maartenvg

Make blogname and tagline editable for everyone. Not only the administrator anymore.

Simple General Settings

Make blogname and tagline editable for everyone. Not only the administrator anymore.

Custom Taglines vs Simple General Settings