Mathematics
Q&A for people studying math at any level and professionals in related fields
Server Fault
Q&A for professional system and network administrators
Graphic Design
Q&A for professional graphic designers and non-designers trying to do their own graphic design
Programmers
Q&A for professional programmers interested in conceptual questions about software development
Electrical Engineering
Q&A for electronics and electrical engineering professionals, students, and enthusiasts
Area 51
Stack Exchange Network staging zone, where users come together to build new Q&A sites
English Language & Usage
Q&A for linguists, etymologists, and serious English language enthusiasts
WordPress Answers
Q&A for WordPress developers and administrators
Stack Apps
Q&A for apps, scripts, and development with the Stack Exchange API
Physics
Q&A for active researchers, academics and students of physics
Photography
Q&A for professional, enthusiast and amateur photographers
Android Enthusiasts
Q&A for enthusiasts and power users of the Android operating system
Database Administrators
Q&A for database professionals who wish to improve their database skills and learn from others in the community
TeX - LaTeX
Q&A for users of TeX, LaTeX, ConTeXt, and related typesetting systems
Cross Validated
Q&A for statisticians, data analysts, data miners and data visualization experts
Meta Stack Overflow
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Theoretical Computer Science
Q&A for theoretical computer scientists and researchers in related fields
Unix & Linux
Q&A for users of Linux, FreeBSD and other Un*x-like operating systems.
Game Development
Q&A for professional and independent game developers
User Experience
Q&A for user experience researchers and experts
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