Stack Overflow
Q&A for professional and enthusiast programmers
Mathematics
Q&A for people studying math at any level and professionals in related fields
Ask Ubuntu
Q&A for Ubuntu users and developers
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
Super User
Q&A for computer enthusiasts and power users
Physics
Q&A for active researchers, academics and students of physics
Mi Yodeya
Q&A for those who base their lives on Jewish law and tradition and anyone interested in learning more
Database Administrators
Q&A for database professionals who wish to improve their database skills and learn from others in the community
Personal Finance & Money
Q&A for people who want to be financially literate
Ask Different
Q&A for power users of Apple hardware and software
Software Engineering
Q&A for professionals, academics, and students working within the systems development life cycle
Server Fault
Q&A for system and network administrators
Information Security
Q&A for information security professionals
Quantitative Finance
Q&A for finance professionals and academics
Meta Stack Exchange
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Area 51
Q&A for proposing new sites in the Stack Exchange network