Akismet: http://akismet.com/

amr users: http://wordpress.org/plugins/amr-users/

Captcha: http://bestwebsoft.com/plugin/:

Facebook: http://wordpress.org/plugins/facebook/

Jetpack by WordPress.com:http://www.cozmoslabs.com/2011/04/12/wordpress-profile-builder-a-front-end-user-registration-login-and-edit-profile-plugin/

Profile Builder: http://www.cozmoslabs.com/2011/04/12/wordpress-profile-builder-a-front-end-user-registration-login-and-edit-profile-plugin/

WP Super Cache: http://ocaoimh.ie/wp-super-cache/

All in one Facebook Plugins for WordPress: http://www.w3xperts.com/all-in-one-facebook-plugins-for-wordpress/

 

Always Remember Me: http://ozh.org/

 

WP-Member:  http://rocketgeek.com/

 

Categories to Tags Converter Importer: http://wordpress.org/extend/plugins/wpcat2tag-importer/

Category Checklist Tree:http://scribu.net/wordpress/category-checklist-tree

 

Custom Contact Forms: http://taylorlovett.com/wordpress-plugins

 

DB-Toolkit: http://dbtoolkit.co.za/

Email Login: http://dentedreality.com.au/projects/wp-plugin-email-login/

 

Email Users: http://wordpress.org/extend/plugins/email-users/

 

Event Espresso Lite - Event Registration and Management: http://eventespresso.com/

Global Hide/Remove Admin Bar Plugin: http://fischercreativemedia.com/wordpress-plugins/global-hide-admin-bar-plugin/

 

Gravity Forms Toolbar:http://genesisthemes.de/en/wp-plugins/gravity-forms-toolbar/

 

Job Manager:http://pento.net/projects/wordpress-job-manager-plugin/

 

User Switching:http://lud.icro.us/wordpress-plugin-user-switching/

 

Viper's Video Quicktags: http://www.viper007bond.com/wordpress-plugins/vipers-video-quicktags/

 

WordPress MU Domain Mapping: http://ocaoimh.ie/wordpress-mu-domain-mapping/