Useful plug-ins

Database related

• HyperDB for advanced database use in Wordpress.
  

Internationalisation

• qTranslate for multilingual support.
  

Roles and Capabilities

• The User role editor by Garagulya, and its Wordpress plug-in page.
• Members by Justin Tadlock.
• Role scoper by Kevin Behrens, and its Wordpress plug-in page
• User access manager
• Advanced access manager by Martyniuk.