"When the going gets tough, the tough get empirical"
-- Jon Carroll
Ask Different
Q&A for power users of Apple hardware and software
Game Development
Q&A for professional and independent game developers
Area 51
Stack Exchange Network staging zone, where users come together to build new Q&A sites
Server Fault
Q&A for professional system and network administrators
User Experience
Q&A for user experience researchers and experts
Electrical Engineering
Q&A for electronics and electrical engineering professionals, students, and enthusiasts
Android Enthusiasts
Q&A for enthusiasts and power users of the Android operating system
WordPress Answers
Q&A for WordPress developers and administrators
Cross Validated
Q&A for statisticians, data analysts, data miners and data visualization experts
Theoretical Computer Science
Q&A for theoretical computer scientists and researchers in related fields
Meta Stack Overflow
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Programmers
Q&A for professional programmers interested in conceptual questions about software development
Stack Apps
Q&A for apps, scripts, and development with the Stack Exchange API
Mathematics
Q&A for people studying math at any level and professionals in related fields
Physics
Q&A for active researchers, academics and students of physics
Role-playing Games
Q&A for gamemasters and players of tabletop, paper-and-pencil role-playing games
Answers OnStartups
Q&A for entrepreneurs looking to start or run a new business
Robotics
Q&A for professional robotic engineers, hobbyists, researchers and students
Programming Puzzles & Code Golf
Q&A for programming puzzle enthusiasts and code golfers