Here I include some references to some cool webpages.
Professors webpages/blogs:
Gerard t'Hooft's webpage and his other page How to become a GOOD Theorist.
Terence Tao's blog, specially his Career Advice page.
Web books and Video-classes/Seminar Channels:
IMPA's recorded courses, most in Portuguese.
PIRSA, Perimeter Institute Recorded Seminar Archive.
For searching articles and authors:
Arxiv -> Acessible pre-prints of Physics, Math and Computer Science articles
InspireHEP -> High Energy Physics research platform
MathSciNet -> American Mathematical Society's gateway for mathematical articles
zbMath -> A tool for finding math articles.
Trivia and Tools:
Paperscape, basically a map of arxiv's articles.
Colorbrewer, good for creating color pallettes for graphs and diagrams.
Project Euler, a page with mathematical/computer science challenges.
Cryptopals, a page for learning cryptography with a  problem-solving approach.
xkcd, THE science comics page.
The Thesis Whisperer, blog on academic writing.