Stack Overflow
Q&A for professional and enthusiast programmers
Cross Validated
Q&A for statisticians, data analysts, data miners and data visualization experts
Science Fiction & Fantasy
Q&A for science fiction and fantasy enthusiasts
Mathematics
Q&A for people studying math at any level and professionals in related fields
English Language & Usage
Q&A for linguists, etymologists, and serious English language enthusiasts
Quantitative Finance
Q&A for finance professionals and academics
Linguistics
Q&A for professional linguists and others with an interest in linguistic research and theory
Physics
Q&A for active researchers, academics and students of physics
Area 51
Stack Exchange Network staging zone, where users come together to build new Q&A sites
User Experience
Q&A for user experience researchers and experts
Programmers
Q&A for professional programmers interested in conceptual questions about software development
Server Fault
Q&A for professional system and network administrators
TeX - LaTeX
Q&A for users of TeX, LaTeX, ConTeXt, and related typesetting systems
Theoretical Computer Science
Q&A for theoretical computer scientists and researchers in related fields
Meta Stack Overflow
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Answers OnStartups
Q&A for entrepreneurs looking to start or run a new business
Writers
Q&A for authors, editors, reviewers, professional writers, and aspiring writers
German Language & Usage
Q&A for speakers of German wanting to discuss the finer points of the language and translation
