I'm an assistant professor in mathematics at Indiana and an early adopter of Math Overflow. I was the first user at mathematics.SE.
Mathematics
Q&A for people studying math at any level and professionals in related fields
Academia
Q&A for academics and those enrolled in higher education
Biblical Hermeneutics
Q&A for professors, theologians, and those interested in exegetical analysis of biblical texts
Biology
Q&A for biology researchers, academics, and students
Meta Stack Overflow
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Theoretical Computer Science
Q&A for theoretical computer scientists and researchers in related fields
Area 51
Stack Exchange Network staging zone, where users come together to build new Q&A sites
English Language & Usage
Q&A for linguists, etymologists, and serious English language enthusiasts
Physics
Q&A for active researchers, academics and students of physics
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
Ask Different
Q&A for power users of Apple hardware and software
Mi Yodeya
Q&A for those who base their lives on Jewish law and tradition and anyone interested in learning more
Cross Validated
Q&A for statisticians, data analysts, data miners and data visualization experts
Board & Card Games
Q&A for people who like playing board games, designing board games or modifying the rules of existing board games
Homebrewing
Q&A for dedicated home brewers and serious enthusiasts