Below are some interesting links to websites that I have found useful as a PhD student and some interesting review papers to read.
ADS – search engine for papers
Astrobites – blog written by various post-graduate students on the latest papers on the arxiv
arXiv – pre-print academic papers
Galaxy clusters in X-ray – Rosati+2002,
draw.io – online diagram software
HMFcalc – online halo mass function calculator
Web plot digitizer – tool to extract data points from figures/plots