Akismet

Possibly the best way in the world to protect you from web spam.

All In One SEO Pack

Optimizes your WordPress blog for Search Engines.

Inline PHP

The plugin can execute php string in posts/pages, and display the output as the contents of posts/pages.

PHP Code Widget

The normal Text widget allows you to insert arbitrary Text and/or HTML code. This allows that too, but also parses any inserted PHP code and executes it.

Sociable

Automatically add links to your favorite social bookmarking sites on your posts, pages and in your RSS feed.

WPtouch

WPtouch automatically transforms your WordPress blog into an iPhone application-style theme, complete with ajax loading articles and effects, when viewed from iPhone, iPod touch, Android, Palm Pre, Samsung touch and BlackBerry Storm/Torch mobile devices.

WP-DBManager

Allows you to optimize database, repair database, backup database, restore database, delete backup database , drop/empty tables and run selected queries. Supports automatic scheduling of backing up and optimizing of database.

WP-Cache

WP-Cache is an extremely efficient WordPress page caching system to make you site much faster and responsive.