Stack Overflow
Q&A for professional and enthusiast programmers
Super User
Q&A for computer enthusiasts and power users
English Language & Usage
Q&A for linguists, etymologists, and serious English language enthusiasts
Open Source
Q&A for people organizing, marketing or licensing open source development projects
Stack Apps
Q&A for apps, scripts, and development with the Stack Exchange API
Code Golf
Q&A for programming puzzle enthusiasts and code golfers
Meta Stack Exchange
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Puzzling
Q&A for those who create, solve, and study puzzles
Graphic Design
Q&A for Graphic Design professionals, students, and enthusiasts
Server Fault
Q&A for system and network administrators
Unix & Linux
Q&A for users of Linux, FreeBSD and other Un*x-like operating systems
Ask Ubuntu
Q&A for Ubuntu users and developers
Photography
Q&A for professional, enthusiast and amateur photographers