Mathematics
Q&A for people studying math at any level and professionals in related fields
Japanese Language
Q&A for students, teachers, and linguists wanting to discuss the finer points of the Japanese language
TeX - LaTeX
Q&A for users of TeX, LaTeX, ConTeXt, and related typesetting systems
Linguistics
Q&A for professional linguists and others with an interest in linguistic research and theory
Stack Overflow
Q&A for professional and enthusiast programmers
Ask Different
Q&A for power users of Apple hardware and software
Meta Stack Exchange
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Philosophy
Q&A for those interested in the study of the fundamental nature of knowledge, reality, and existence
Academia
Q&A for academics and those enrolled in higher education
Mi Yodeya
Q&A for those who base their lives on Jewish law and tradition and anyone interested in learning more
Area 51
Q&A for proposing new sites in the Stack Exchange network