Plugin modules add a specific feature or service to the WordPress system.
Event Calendar manage future events as an online calendar. Display upcoming events in a dynamic calendar, on a listings page, or as a list in the sidebar. You can subscribe to the calendar from iCal (OSX) or Sunbird. Also adds sidebar widgets for Event Calendar and Upcoming Events. Requires the EventCalendar and Widget plugins.
Insights allows you to quickly access and insert information (links, images, videos, maps..) into your blog posts.
NextGEN Gallery photo gallery for the Web 2.0.
Really Simple CAPTCHA is a module intended to be called from other plugins. Reduces spam.
SexyBookmarks adds a (X)HTML compliant list of social bookmarking icons to each of your posts.
FancyBox for WordPress all images on a page are treated as a gallery allowing to use Next and Previous buttons on the FancyBox frontend.
WordPress Database Backup on-demand backup of your WordPress database.
WP-iGoogle create a dynamic Google gadget for your Blog. People can add your gadget to iGoogle or to their other pages across the web. When users add your gadget to their iGoogle homepage, they’ll see your content each time they visit Google.
WP-Insert Manage Ads, Feeds, Tracking etc
Akismet checks your comments against the Akismet web service to see if they look like spam or not. You need a WordPress.com API key to use it. You can review the spam it catches under “Comments.” See also: WP Stats plugin.