Sites/Blogs that I visit often:

• MTTS - A treasure for mathematics students and teachers in India (MTTS pamphlet).

• Gametheory.net - A site with interesting resources for learning/teaching Game Theory 

• Quanta Magazine - A magazine with exciting scientific writings. 

• Mind Your Decisions - Presh Talwalkar's blog has many mature mathematical questions that people of all domains could try.

• The illustrated guide to a Ph.D. - Prof. Matt Might's fascinating illustrated guidance.

• Eluththu (Tamil) - A library of interesting literature and linguistics of Tamil.