Lifestream plugin for WordPress that gives you a tumblr-esque activity stream aggregated from multiple locations. Slick.
aMember is a membership management script in PHP. It integrates with multiple payment gateways, handles secure access, integrates with WordPress, Joomla, vBulletin, etc. Looks useful. $180.
The WordPress WP-Cache2 caching plugin / platform. The plugin caches WordPress to static files and then serves those files instead of rebuilding the pages on every request.
LightPress is a fast, template-based frontend for the popular WordPress blogging platform.
A WordPress plugin that encrypts the admin interface traffic over SSL to increase site security.
This plugin allows you to redirect permalinks to a new location or from an old permalink structure to a new one.