Here are a few of the WordPress plugins I have used for our church website at http://www.cambray.org.

Scripturizer is great for churches that often make references to Bible quotations on their sites, as our church does. It creates links to biblegateway.com.
Pages advanced allows the pages on the site to be searched as well as posts. It is my view that a Church site is best designed with pages for visitors and posts or date entry type pages for the people who are the local church.

There are other WordPress plugins that I must arrange to try out properly as I can see their usefulness, these include :

Sorry about the typeface changes above. Copy pasting rather than typing in the information!

We are still trying to crack various challenges with sermon mp3s and the best plugin to podcast the sermons so I have not included them here yet.

Pages Advanced 1.0 Advanced options for Pages. Includes Search Pages by David B. Nagle and Page Restriction by James Asher. More info… By Dave Mitchell .
Admin Simplified 2.2 Terms of useDoc/FAQSupport forum — Removes some of the cruft in the admin interface. By Denis de Bernardy .
Static Front Page 2.4 Terms of useDoc/FAQSupport forum — Sticks the page with a slug of ‘home’ to your front page. By Denis de Bernardy .
Scripturizer 1.5 Changes Bible references to hyperlinks for WordPress 1.5 and above. If you have a higher version of WordPress you might want to upgrade the plugin. By Dean Peters, ported by Glen Davis, updated by LaurenceO.com .
Site Meter 1.01 This plugin allows you to easily add Site Meter tracking to your pages. By David Smith .