MathDL 
Mathematical Association of America’s Mathematical Sciences Digital Library

Mathematics on the Web 
American Mathematical Society (AMS)

ViFaMATH 
Virtuelle Fachbibliothek Mathematik  - SUB Göttingen

arXiv.org
Open access preprints in Physics, Mathematics, Computer Science, Cornell University Library, Ithaka, NY

Digitization Registry 
SUB Göttingen. The Digitisation Registry provides information about digitisation projects and access to digitized materials.

The Electronic Library of Mathematics 
EMS; free online journals, article collections, and monographs in the field of mathematics

EuDML: The European Digital Mathematics Library
EuDML by 15 partners from 9 European countries. Over 200'000 documents from scholarly journals, monographs, and multivolume works, scientifically validated and eventually open access.

European Mathematical Information Service EMIS 
European Mathematical Society (EMS) - u.a. Testzugänge zu MATH (Zentralblatt) und MATHDI

MacTutor History of Mathematics archive 
University of St Andrews, Scotland - a integrated collection of over 1000 biographies and historical articles

Mathematical functions 
über 37000 mathematische Formeln und Funktionen

Mathematics Books Online 
AMS, frei zugängliche Online-Mathematikbücher

Metamaths 
Norman Megill (MIT), maschinelle Verifikation von Beweisen

swiss electronic academic library service 
Commentarii Mathematici Helvetici 1929-1996, L'Enseignement Mathématique 1899-2000