University of Michigan Historical Mathematics Collection
- A digital library of books selected from the University of Michigan mathematics collection, published in the 19th or early 20th century.
- http://quod.lib.umich.edu/u/umhistmath/

EJDE Monographs
- Textbooks and expository articles hosted by the Electronic Journal of Differential Equations.
- http://ejde.math.txstate.edu/mono-toc.html

NUMerisation de Documents Anciens Mathematiques
- Digitized ancient mathematical documents in Grenoble.
- http://www.numdam.org/

EMIS Mathematical Monographs
- Books hosted by the European Mathematical Information Service in various formats, typically PostScript, but sometimes also DVI and PDF.
- http://www.emis.de/monographs/

Online Notes
- A collection of links to online notes maintained by Boris Levant at the Weizmann Insitute.
- http://www.wisdom.weizmann.ac.il/~borisl/online_notes.html

MATHnetBASE
- Commercial library of mathematics texts and articles from CRC/Chapman and Hall. Annual subscription required.
- http://www.mathnetbase.com/

Math eBooks
- Commercial solved-problem guides on various math topics in PDF format.
- http://www.math-ebooks.com/

Gallica
- A digital collection of classics from the National Library of France.
- http://gallica.bnf.fr/

Mathematica
- A collection of classical manuscripts (mostly in German) at the Center for Retrospective Digitization in Goettingen.
- http://gdz.sub.uni-goettingen.de/en/

Electronic Research Archive for Mathematics
- A digital library for classical mathematics.
- http://www.emis.de/projects/JFM/

The Assayer
- Features online books and articles on math, computer and science topics by a variety of authors. Includes some reader reviews.
- http://www.theassayer.org/cgi-bin/asbrowsesubject.cgi?class=Q

MathPages
- A collection of HTML lectures on various subjects in mathematics and physics.
- http://www.mathpages.com/

Books On-line: QA
- Online Books page at the University of Pennsylvania.
- http://digital.library.upenn.edu/webbin/book/subjectstart?QA

Geometry & Topology Monographs
- A series intended for research monographs, for refereed conference proceedings, and for similar collections.
- http://www.maths.warwick.ac.uk/gt/gtmono.html

Electronic Books and Journals
- Links maintained by the University of Haifa.
- http://math.haifa.ac.il/ejournals.html

Mathematics Archives - Topics
- Links to books, notes and other resources organized by topic at the University of Tennessee, Knoxville.
- http://archives.math.utk.edu/topics/

ICTP Lecture Notes Series
- Paedagogical material in advanced topics from the Abdus Salam International Centre for Theoretical Physics, Trieste. LaTeX and PostScript.
- http://www.ictp.trieste.it/~pub_off/lectures/

arXiv
- E-print archive in various areas of physics, mathematics, nonlinear science, and computer science.
- http://arxiv.org/

Mathwright Library
- A free collection of interactive mathematics and science books. Requires free (Windows) software to read.
- http://www.mathwright.com/

AMS Books Online
- AMS published books available for free download in PDF. Also links to other online books.
- http://www.ams.org/online_bks/

Online Mathematics Textbooks
- Links to online mathematics texts, maintained by George Cain at Georgia Institute of Technology.
- http://www.math.gatech.edu/~cain/textbooks/onlinebooks.html

Mathphysics.com
- This site exists primarily to host on-line textbooks and other scholarly materials in mathematics or physics.
- http://www.mathphysics.com/

Maths at sigma.ndo.co.uk
- Lecture notes for various courses taught at the Univ. of Birmingham.
- http://www.sigma.ndo.co.uk/maths/