Automattic Kismet (Akismet for short) is a collaborative effort to make comment and trackback spam a non-issue and restore innocence to blogging, so you never have to worry about spam again. Amazing spam filter for comments. If you do not have it, you will be spammed like hell.

WP-Cache is an extremely efficient WordPress page caching system to make your site much faster and responsive. It works by caching Worpress pages and storing them in a static file for serving future requests directly from the file rather than loading and compiling the whole PHP code and then building the page from the database. WP-Cache allows to serve hundred of times more pages per second, and to reduce the response time from several tenths of seconds to less than a millisecond.

AdSense-Deluxe is a WordPress plugin offering advanced options for managing the automatic insertion of Google AdSense or Yahoo Publisher Network (YPN) ads to your WordPress posts.

Without it, its a pain to add adsense ads to your posts.

Digg this wordpress plugin is a plugin that detects incoming links from Digg.com to your wordpress post and automatically display a link back to the digg post, for people to digg your story.

Simplifies the whole process of digging.

The WP-DB-Backup : WP-DB-Backup allows you easily to backup your core WordPress database tables. The backups are really handy if your server goes down. A must for all bloggers.