Google Scholar is a search engine for academic publications and also provides citation counts.
AMS MathSciNet is an online bibliographic reference for mathematical journal articles and publications. (Subscription required)
AMS MR Citation Database lists a person's most cited mathematical publications. (Subscription required)
Mathematics ArXiv is an online repository of mathematical preprints (articles that are not yet published in a journal or book).
The Mathematics Genealogy Project shows the mathematical ancestors and descendants of a mathematician.
Institute for Advanced Study is one of the world's leading centers for theoretical research, especially pure mathematics.
Mathematical Sciences Research Institute is an NSF-funded institute located in Berkeley, California.
Clay Mathematics Institute is a privately funded foundation dedicated to supporting mathematical research and disseminating mathematics. It is best known for posing the Millennium Problems setting a $1 million prize for the first solution to each problem.
American Institute of Mathematics is a privately funded research institute in Palo Alto, California.
Institut des Hautes Etudes Scientifiques located in Bures-sur-Yvette, France (just outside Paris) is one of the world's leading mathematical research institutes.
