Optimization-online – Repository of e-prints about optimization and related topics.
COIN-OR – Initiative to spur the development of open-source software for the operations research community.
Khan Academy – Learn anything for free!
Code Academy – Start coding now!
N is a Number – A Portrait of Paul Erdős – Documentary.
Mário Sergio Cortella – Qual a postura ideal do professor? – Lecture of the professor and philosopher Mario Sergio Cortella (in portuguese).
Audiofanzine – Music & audio.
Deviantart – Art community.