Stack Overflow
Q&A for professional and enthusiast programmers
Meta Stack Overflow
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Japanese Language & Usage
Q&A for students, teachers, and linguists wanting to discuss the finer points of the Japanese language
Area 51
Stack Exchange Network staging zone, where users come together to build new Q&A sites
Programmers
Q&A for professional programmers interested in conceptual questions about software development
Server Fault
Q&A for professional system and network administrators
Mathematics
Q&A for people studying math at any level and professionals in related fields
Theoretical Computer Science
Q&A for theoretical computer scientists and researchers in related fields
English Language & Usage
Q&A for linguists, etymologists, and serious English language enthusiasts
Unix & Linux
Q&A for users of Linux, FreeBSD and other Un*x-like operating systems.
Electrical Engineering
Q&A for electronics and electrical engineering professionals, students, and enthusiasts
Database Administrators
Q&A for database professionals who wish to improve their database skills and learn from others in the community
Game Development
Q&A for professional and independent game developers
Physics
Q&A for active researchers, academics and students of physics
User Experience
Q&A for user experience researchers and experts
Stack Apps
Q&A for apps, scripts, and development with the Stack Exchange API
Personal Finance & Money
Q&A for people who want to be financially literate
Programming Puzzles & Code Golf
Q&A for programming puzzle enthusiasts and code golfers
Cryptography
Q&A for software developers, mathematicians and others interested in cryptography
Board & Card Games
Q&A for people who like playing board games, designing board games or modifying the rules of existing board games