Javascript, PHP, C++, CSS, .htaccess, HTML (XHTML), MySQL (and other *SQLs)
Stack Overflow
Q&A for professional and enthusiast programmers
Physics
Q&A for active researchers, academics and students of physics
Electrical Engineering
Q&A for electronics and electrical engineering professionals, students, and enthusiasts
Meta Stack Overflow
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
French Language & Usage
Q&A for students, teachers, and linguists wanting to discuss the finer points of the French language
Area 51
Stack Exchange Network staging zone, where users come together to build new Q&A sites
Unix & Linux
Q&A for users of Linux, FreeBSD and other Un*x-like operating systems.
Mathematics
Q&A for people studying math at any level and professionals in related fields
Web Applications
Q&A for power users of web applications
Programmers
Q&A for professional programmers interested in conceptual questions about software development
Server Fault
Q&A for professional system and network administrators
Game Development
Q&A for professional and independent game developers
English Language & Usage
Q&A for linguists, etymologists, and serious English language enthusiasts
User Experience
Q&A for user experience researchers and experts
Computer Science
Q&A for students, researchers and practitioners of computer science
Raspberry Pi
Q&A for users and developers of hardware and software for Raspberry Pi