Penn State Center for Gravitational Physics and Geometry

Online seminars in streaming audio discussing current topics in relativity theory, relativity cartoons and other resources

Relativity on the World Wide Web

Relativity tutorials, online courses, articles, visualizations and commentary.

Max Planck Institute for Gravitational Physics

A private institute devoted to theoretical research into general relativity and gravitationd

 

While not specific to relativity, the next few links are excellent
sources of information and a good way to stay current on various physics and other scientific topics

AIP Weekly Physics News

A variety of current topics in modern physics

Scientific American

Scientific articles written for the public by various researchers

Science News 

Weekly newsmagazine on current research

Sci-Hub  

Open Access to Paywalled Research

Libgen.io  

Open Access to Scientific Textbooks