X.com: 
Facebook: 
YouTube: 
These are links that I find useful for work-related purposes.
Funding Agencies
- Fetzer Franklin Fund —
- FQXi — Foundational Questions in Physics and Astronomy.
- John Templeton Foundation —
Job Listings
- APS Jobs site — American Physical Society careers site.
- Physics World Jobs — Institute of Physics job search site.
- Quantiki Jobs Page — Wiki job listings.
- Quantum Information Processing Jobs — Job listing site maintained by Todd Brun.
Mathematics
- The Mathematics Genealogy Project — Traces Ph.D. supervisor relationships of mathematicians.
- Wolfram Alpha — Computational Intelligence
- Wolfram MathWorld — Mathematics Encyclopedia.
Philosophy
- Stanford Encyclopedia of Philosophy — Has articles on most topics in quantum foundations.
Quantum Groups of Professional Physics Societies
- Division of Quantum Information — American Physical Society.
- Quantum Information, Quantum Optics and Quantum Control Group — Institute of Physics.
Research Articles
- The arXiv preprint archive — Most quantum physics/maths/computer science papers are posted here before publication.