There are now over 375 Drupal Groups and 23533 groups subscribers. The following 14 groups may be of particular interest to Non Governmental Organizations who are using or planning to use Drupal for their infrastructure:

General Business

Drupal for Activists and Campaigns, 109 subscribers
Issues and ideas relating to the use of Drupal by activists and campaigners
http://groups.drupal.org/drupal-for-activists-and-campaigns

Drupal for Good, 222 subscribers
Group for those using Drupal in the nonprofit world
http://groups.drupal.org/drupal-for-good

Consulting and Business, 409 subscribers
Consultants and businesses that use and develop with Drupal
http://groups.drupal.org/consulting

Drupal Camp, 162 subscribers
The main group for all Drupal Camp organizing
http://groups.drupal.org/drupal-camp

Marketing & Communications

Advertising, 151 subscribers
Discuss advertising and Drupal sites.
http://groups.drupal.org/advertising

Analytics, 135 subscribers
Discuss user data tracking and analysis using Drupal and third party tools.
http://groups.drupal.org/analytics

Building Site Traffic, 111 subscribers
Modules and techniques to help promote and drive traffic to your Drupal-based site
http://groups.drupal.org/building-site-traffic

Site Design

Accessibility, 121 subscribers
Working on making Drupal more accessible to users with disabilities and unusual browsers
http://groups.drupal.org/accessibility

Designers and Information Architects, 281 subscribers
A group for Drupal users to discuss the design of Drupal powered sites
http://groups.drupal.org/designers-and-information-architects

Translations, 177 subscribers
Translation and internationalization of Drupal
http://groups.drupal.org/translations

Usability, 194 subscribers
Help make Drupal much more easy to use
http://groups.drupal.org/usability

Relationship & Community Building

Community, 346 subscribers
As in community building. How to go about it. How to do it with Drupal. Etc
http://groups.drupal.org/community

CiviCRM, 227 subscribers
Using the CiviCRM Relationship Management System and Drupal
http://groups.drupal.org/civicrm

Social Networking Sites, 436 subscribers
Sites that aim to connect people and the modules that make it possible.
http://groups.drupal.org/social-networking-sites

Please feel free to post any additions in the comments below.