WordPress Database Backup
Thanks to WordPress’s built-in cron, this popular plugin allows users to schedule automatic database backups.
Comments Preview
Let your commenters preview their comments before posting. It doesn’t require JavaScript, and the previewed comments have all the relevant filters applied to them so that commenters can see exactly how their comments will look when published.
Custom Appearance Date
Show a post on a date different from its publish date.
Custom Image Sizes
Generate custom thumbnails of attachments on demand.
Delayed Email Plugin
WP Delayed Mail lets you send an email at a future time.
Tinfoil-hat
Check for new versions of WordPress and your plugins without sending a list of all plugins associated with your URL.
Gravatar
Use Gravatars with clean theme code and easy customization.
Enroll in Comments
Lets commenters check a subscription box to subscribe to comments, and it creates “subscriber” accounts for them. Users can manage their subscriptions (both to enroll and un-enroll) by logging in to WordPress.
Categories in Tag Cloud
Include your categories the WordPress tag cloud.
Home-Page Control
Turn WordPress into a content management system, by choosing which of your pages to be the home page. Put the blog posts home page in a customized directory.
JavaScript Extract
Make image title attributes into visible captions, and turn blockquote cite attributes into source reference links, using the efficiency of JavaScript.
Old-Style Upload
Restores for WordPress 2.0 the uploading feature found in previous versions.
Uncheck Default Category
When you check another category in your post’s list, it unchecks your default category.
Hide Email Addresses
Uses JavaScript to hide from spambots any email addresses embedded within posts and pages.
Google AdSense Section Targeting
Tell Google AdSense spiders what to pay particular attention to and what to ignore, when generating Google ads for your site.
Highlight Category
Only for WordPress versions before 2.0, as this became a core feature, this plugin inserts the class “current-cat” into the link for a category, if someone’s browsing the archives under that category.