A general reference for mathematical resources is the page "Mathematics on the Web" maintained by the AMS.

Articles/Books Online

• AMS directory of preprints servers
• AMS directory of electronic books
• arXiv.org
• JSTOR
• NUMDAM
• E-Journals and reference databases at CUNY
• Digital Mathematics Library

Authors' Tools

• MathSciNet
• 2000 Mathematics Subject Classification
• Math Reviews Lookup
• LaTeX resources at TUG
• The comprehensive LaTeX symbol list
• AMS index of mathematical softwares

Libraries

• CUNY Libraries
• Columbia Libraries
• NYU Libraries
• New York City Public Library

Institutions

• Department listing of local seminars.
• AMS directory of mathematics departments in North America
• PSU directory of mathematics departments around the world
• Fields Institute (Toronto)
• IAS (Princeton)
• ICTP (Trieste)
• IHES (Paris)
• IMA (Minnesota)
• IMS (Stony Brook)
• Max-Planck (Bonn)
• MFO (Oberwolfach)
• MSRI (Berkeley)
• Newton Institute (Cambridge)

Organizations

• American Mathematical Society
• European Mathematical Society
• International Mathematical Union
• Mathematical Association of America
• NSF Division of Mathematical Sciences
• CUNY Research Foundation

Miscellaneous

• Mathematics Genealogy Project
• History of Mathematics Archive
• Virtual Mathematics Museum