Stack Overflow
Q&A for professional and enthusiast programmers
Area 51
Stack Exchange Network staging zone, where users come together to build new Q&A sites
Physical Fitness
Q&A for physical fitness professionals, athletes, trainers, and those providing health-related needs
Drupal Answers
Q&A for Drupal developers and administrators
Biology
Q&A for biology researchers, academics, and students
Mathematics
Q&A for people studying math at any level and professionals in related fields
Photography
Q&A for professional, enthusiast and amateur photographers
Ask Different
Q&A for power users of Apple hardware and software
User Experience
Q&A for user experience researchers and experts
Programmers
Q&A for professional programmers interested in conceptual questions about software development
Database Administrators
Q&A for database professionals who wish to improve their database skills and learn from others in the community
Meta Stack Overflow
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Science Fiction & Fantasy
Q&A for science fiction and fantasy enthusiasts
French Language & Usage
Q&A for students, teachers, and linguists wanting to discuss the finer points of the French language
Biblical Hermeneutics
Q&A for professors, theologians, and those interested in exegetical analysis of biblical texts
Christianity
Q&A for committed Christians, experts in Christianity and those interested in learning more
Personal Productivity
Q&A for people wanting to improve their personal productivity
Personal Finance & Money
Q&A for people who want to be financially literate
Computational Science
Q&A for scientists using computers to solve scientific problems
Answers OnStartups
Q&A for entrepreneurs looking to start or run a new business